Patent Publication Number: US-2010121490-A1

Title: Base sequence detection apparatus and base sequence automatic analyzing apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation application of Ser. No. 11/045,646, filed Jan. 31, 2005, which is a Continuation Application of PCT Application No. PCT/JP03/09684, filed Jul. 30, 2003, which was published under PCT Article 21(2) in Japanese, the entire contents of both of which are incorporated herein by reference. 
    
    
     This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2002-223392, filed Jul. 31, 2002; and No. 2003-200440, filed Jul. 23, 2003, the entire contents of both of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a base sequence detection apparatus which detects a base sequence and a base sequence automatic analyzing apparatus which automatically controls the base sequence detection apparatus and automatically analyzes a measurement signal. 
     2. Description of the Related Art 
     There conventionally exist, e.g., apparatuses which execute only hybridization, apparatuses which execute only electrochemical measurement after hybridization and addition of intercalating agents, and apparatuses which automatically execute a whole process from hybridization to cleaning using buffers (e.g., patent document 1: Jpn. Pat. Appln. KOHYO Publication No. 9-504910). 
     Assume that measurement is executed by using the above-described apparatuses. Every time one process is ended, the operator must manually transfer the sample to the apparatus for the next process. This imposes restrictions on time. In addition, since the operator takes a hand in transfer between processes, the data reproducibility between samples is poor. 
     Furthermore, measurement results may vary depending on reaction conditions in a reaction cell. When measurement is performed using a 3-electrode unit including a plurality of working electrodes, the reaction environment varies between the working electrodes, and therefore, detection results also vary. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a base sequence detection apparatus which has a highly uniform electrochemical reaction characteristic and a high detection reliability. 
     It is another object of the present invention to provide a base sequence automatic analyzing apparatus which can automatically execute a whole process of reaction, solution supply, and measurement. 
     According to an aspect of the present invention, there is provided a base sequence detection apparatus which detects a first base sequence in a sample on the basis of a reaction between the sample in a channel and a probe including a second base sequence, comprising a substrate, a channel which is formed on the substrate along a flowing direction of a biochemical solution or air, a plurality of working electrodes which are formed on the substrate along the channel and include the probe immobilized thereon, a plurality of counter electrodes which are formed on an inner surface of the channel in correspondence with the working electrodes and located on a first surface opposing a surface of the substrate to give a potential difference with respect to the working electrodes, a plurality of reference electrodes which are formed on an inner surface of the channel in correspondence with the working electrodes and located on a second surface opposing the substrate surface to feedback a detection voltage to the working electrodes, an introduction port which is open to the channel and introduces the biochemical solution or air into an upstream side of the channel into the channel, a delivery port which is open to the channel and delivers the biochemical solution or air from a downstream side of the channel; and a sample injection port through which the sample is injected into the channel. 
     According to another aspect of the present invention, there is provided a base sequence detection apparatus which detects a first base sequence in a sample on the basis of a reaction between a probe including a second base sequence and the sample in a cell which is defined by a cell upper surface, cell side surfaces, and a cell bottom surface, comprising: 
     a base sequence detection chip which comprises a substrate and a plurality of working electrodes and defines the cell bottom surface, wherein the working electrodes are formed on the substrate along a flowing direction of a biochemical solution or air and having the probe immobilized thereon; 
     a chip cartridge top cover which comprises counter electrodes and reference electrodes formed along the flowing direction of the biochemical solution or air, wherein the counter electrodes are formed in correspondence with the working electrodes and located on a first surface opposing a surface of the substrate to give a potential difference with respect to the working electrodes, and the reference electrodes are formed in correspondence with the working electrodes and located on a second surface opposing the substrate surface to feedback a detection voltage to the working electrodes; 
     a sealing member which is sandwiched and fixed between the chip cartridge top cover and the substrate surface to form a channel including equal sections near the working electrodes, counter electrodes, and reference electrodes and defines the cell upper surface and cell side surfaces; 
     an introduction port which is formed in the chip cartridge top cover and introduces the biochemical solution or air into an upstream side of the flowing direction of the biochemical solution or air into the cell; 
     a delivery port which is formed in the chip cartridge top cover and delivers the biochemical solution or air in the cell from a downstream side of the flowing direction of the biochemical solution or air; and 
     a sample injection port which is formed in the chip cartridge top cover and through which the sample is injected into the cell. 
     According to get another aspect of the present invention, there is provided a base sequence automatic analyzing apparatus comprising: 
     a base sequence detection apparatus described above; 
     a supply unit comprising a first pipe which communicates with the introduction port and supplies the biochemical solution or air into the channel through the introduction port, and a first valve which controls a flow rate of the biochemical solution or air in the first pipe; 
     a discharge unit comprising a second pipe which communicates with the delivery port and discharges the biochemical solution or air from the channel through the delivery port, a second valve which controls the flow rate of the biochemical solution or air in the second pipe, and a pump which is arranged on the second pipe and sucks the biochemical solution or air from the channel; 
     a measurement unit comprising a voltage applying unit which gives a potential difference between the working electrode and the counter electrode; 
     a temperature controller which controls a temperature of the base sequence detection chip; 
     a control mechanism which controls the first valves of the supply unit, the second valve and pump of the discharge unit, the voltage applying unit of the measurement unit, and the temperature controller, detects an electrochemical reaction signal from the working electrode or counter electrode, and stores the electrochemical reaction signal as measurement data; and 
     a computer which gives control condition parameters to the control mechanism to control the control mechanism and executes analysis processing of the first base sequence on the basis of the measurement data. 
     According to further aspect of the present invention, there is provided a base sequence automatic analyzing apparatus which automatically analyzes a first base sequence in a sample on the basis of a reaction between the sample in a channel and a probe including a second base sequence, comprising: 
     a cassette including 
     a substrate including a major surface and pads on the major surface, 
     a sealing member comprising a sealing member main body which comprises a major surface and a flat lower surface that is arranged in contact with the major surface of the substrate and includes a plurality of working electrodes that are formed on the major surface along the channel wherein the probe is immobilized thereon, reference electrodes and counter electrodes, a groove portion which is formed in the lower surface and forms a gap with respect to the working electrodes to form the channel, a first port which communicates with one end of the channel and is open to the major surface at a first position separated from the major surface of the substrate, and a second port which communicates with the other end of the channel and is open to the major surface at a second position separated from the major surface of the substrate, and 
     a cassette main body which brings the lower surface of the sealing member main body into contact with the major surface of the substrate and fixes the sealing member main body; 
     a valve unit including a first valve which switches between a biochemical solution and air supplied from the first port, a second valve which switches between the biochemical solution and air discharged from the second port, a first nozzle connected to the first valve, and a second nozzle connected to the second valve wherein the first and second valves and the first and second nozzles are integrally formed; 
     a probe unit which is fixed to the valve unit and includes an electric connector; 
     a driving unit which drives the valve unit or the cassette to position the first nozzle to the first port and communicate the first nozzle with the first port, position the second nozzle to the second port and communicate the second nozzle with the second port, and position the electric connector of the probe unit to the pads on the substrate and connect the pads to the electric connector electrically; 
     a measurement mechanism which inputs a measurement signal to the substrate and acquires an electrical signal from the substrate; and 
     a computer which analyzes the electrical signal obtained from the measurement mechanism. 
     The present invention related to the apparatus is also effective as the invention of the method realized by the apparatus. 
     The present invention related to the apparatus or method is also effective as a program which causes a computer to execute procedures for controlling the apparatus and a computer-readable recording medium which records the program. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  is a block diagram showing the overall arrangement of a base sequence detection apparatus according to the first embodiment of the present invention; 
         FIGS. 2A to 2D  are views showing details of the structure of a chip cartridge according to the first embodiment; 
         FIG. 3  is a view showing a support body and a chip cartridge top cover before they are fixed by a top cover fixing screw according to the first embodiment; 
         FIG. 4  is a view showing the detailed structure of a printed board on which a base sequence detection chip according to the first embodiment is mounted; 
         FIGS. 5A to 5C  are views showing a cell and a biochemical solution supply system which communicates with the cell according to the first embodiment; 
         FIGS. 6A and 6B  are views showing a modification of the cell according to the first embodiment; 
         FIGS. 7A and 7B  are views showing a more detailed structure of constituent elements near the cell according to the first embodiment; 
         FIG. 8  is a plan view of the cell according to the first embodiment; 
         FIG. 9  is a plan view of a modification of the cell according to the first embodiment; 
         FIG. 10  is a sectional view of a modification of the shape of the cell according to the first embodiment; 
         FIG. 11  is a sectional view of another modification of the shape of the cell according to the first embodiment; 
         FIG. 12  is a plan view of a modification of a detection channel according to the first embodiment; 
         FIGS. 13A and 13B  are views showing a modification of the structure of the cell according to the first embodiment; 
         FIG. 14  is a view showing an example of the structure of a sealing member according to the first embodiment; 
         FIGS. 15A to 15D  are sectional views showing steps in manufacturing the base sequence detection chip and printed board according to the first embodiment; 
         FIG. 16  is a plan view of the base sequence detection chip according to the first embodiment; 
         FIG. 17  is a view showing a detailed arrangement of a solution supply system according to the first embodiment; 
         FIG. 18  is a flow chart of a solution supply step for base sequence detection using the according to the first embodiment; 
         FIG. 19  is a view showing the detailed arrangement of a measurement system according to the first embodiment; 
         FIG. 20  is a view showing the arrangement of a conventional potentiostat; 
         FIGS. 21A to 21E  are timing charts showing voltage characteristics according to the first embodiment; 
         FIGS. 22A to 22D  are timing charts showing the voltage characteristics of the conventional potentiostat; 
         FIG. 23  is a graph showing current/voltage characteristic curves applied to counter electrodes in a potentiostat according to the first embodiment and the conventional potentiostat; 
         FIG. 24  is a view showing a modification of the potentiostat according to the first embodiment; 
         FIG. 25  is a view showing another modification of the potentiostat according to the first embodiment; 
         FIG. 26  is a view showing still another modification of the potentiostat according to the first embodiment; 
         FIG. 27  is a view showing still another modification of the potentiostat according to the first embodiment; 
         FIG. 28  is a block diagram showing the association between the control mechanism and the remaining constituent elements of a computer according to the first embodiment; 
         FIG. 29  is a block diagram showing a detailed arrangement of the control mechanism according to the first embodiment; 
         FIG. 30  is a flow chart showing an example of a measurement data analyzing method according to the first embodiment; 
         FIG. 31  is a flow chart of type determination filtering processing according to the first embodiment; 
         FIG. 32  is a flow chart showing an example of type determination processing according to the first embodiment; 
         FIG. 33  is a sequence chart of a base sequence automatic analyzing method using the base sequence detection apparatus according to the first embodiment; 
         FIG. 34  is a view showing another modification of the cell according to the first embodiment; 
         FIG. 35  is a view showing the overall arrangement of a base sequence automatic analyzing apparatus according to the second embodiment of the present invention; 
         FIG. 36  is a perspective view of a cassette according to the second embodiment; 
         FIG. 37  is a perspective view of a cassette top cover to the second embodiment; 
         FIG. 38  is a view showing the structure of a cassette bottom cover according to the second embodiment; 
         FIG. 39  is a perspective view of a packing according to the second embodiment; 
         FIG. 40  is a plan view of the packing according to the second embodiment; 
         FIG. 41  is a plan view of a substrate according to the second embodiment; 
         FIG. 42  is a view showing the assembled state of the cassette according to the second embodiment; 
         FIG. 43  is a view showing the assembled state of the cassette according to the second embodiment; 
         FIG. 44  is a sectional view of a cassette side surface according to the second embodiment; 
         FIG. 45  is a view showing details of a channel according to the second embodiment; 
         FIG. 46  is a view showing the detailed structure of a packing tip shape according to the second embodiment; 
         FIG. 47  is a view showing the detailed structure of another packing tip shape according to the second embodiment; 
         FIG. 48  is a view showing the detailed structure of still another packing tip shape according to the second embodiment; 
         FIG. 49  is a view showing the detailed structure of still another packing tip shape according to the second embodiment; 
         FIG. 50  is a view showing the detailed structure of still another packing tip shape according to the second embodiment; 
         FIG. 51  is a view showing the detailed structure of still another packing tip shape according to the second embodiment; 
         FIG. 52  is a view showing the overall arrangement of a valve unit according to the second embodiment; 
         FIG. 53  is a view showing the functional arrangement of the valve unit according to the second embodiment; 
         FIGS. 54A to 54D  are views showing the detailed structures of nozzle tip shapes according to the second embodiment; 
         FIGS. 55A and 55B  are views showing the structures of the packing and nozzle according to the second embodiment; 
         FIG. 56  is a view showing an example of the arrangement of the base sequence automatic analyzing apparatus according to the second embodiment in a cassette loading operation; 
         FIGS. 57A and 57B  are views showing the detailed structure of a probe unit according to the second embodiment; 
         FIG. 58  is a view showing the detailed structures of the probe unit and valve unit according to the second embodiment; 
         FIG. 59  is a view showing a modification of the cassette according to the second embodiment; 
         FIGS. 60A and 60B  are views for explaining a cassette fixing method in the modification of the cassette according to the second embodiment; 
         FIG. 61  is a view showing another example of the valve unit according to the second embodiment; 
         FIG. 62  is a view showing still another example of the valve unit according to the second embodiment; 
         FIG. 63  is a view showing still another example of the valve unit according to the second embodiment; 
         FIG. 64  is a view showing still another example of the valve unit according to the second embodiment; 
         FIG. 65  is a view showing the functional arrangement of another valve unit according to the second embodiment; 
         FIGS. 66A and 66B  are views showing examples of a liquid oscillation mechanism according to the second embodiment; 
         FIGS. 67A and 67B  are views showing examples of the cassette with and without a seal according to the second embodiment; 
         FIG. 68  is a view for explaining a seal detection operation according to the second embodiment; 
         FIGS. 69A and 69B  are views for explaining a cassette detection operation according to the second embodiment; 
         FIG. 70  is a flow chart of measurement preparation processing according to the second embodiment; 
         FIG. 71  is a view for explaining an electrical connection presence/absence determination method according to the second embodiment; 
         FIG. 72  is a flow chart of an automatic analyzing operation according to the second embodiment; 
         FIG. 73  is a functional block diagram of a control mechanism and the remaining constituent elements according to the second embodiment; and 
         FIGS. 74A to 74C  are views showing combination examples of the nozzle and packing according to the second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments of the present invention will be described below with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a block diagram showing the overall arrangement of a base sequence automatic analyzing apparatus according to the first embodiment of the present invention. As shown in  FIG. 1 , a base sequence automatic analyzing apparatus  1  includes a chip cartridge  11  (base sequence detection apparatus), a measurement system  12 , a solution supply system  13 , and a temperature control mechanism  14 . The chip cartridge  11  and measurement system  12  are electrically connected. The solution supply system  13  is physically connected to a channel provided in the chip cartridge  11  through an interface section. The temperature control mechanism  14  controls the temperature of the chip cartridge  11 . 
     The measurement system  12 , solution supply system  13 , and temperature control mechanism  14  are controlled by a control mechanism  15 . The control mechanism  15  is electrically connected to a computer  16 . The control mechanism  15  is controlled in accordance with a program installed in the computer  16 . In this embodiment, the chip cartridge  11 , measurement system  12 , solution supply system  13 , and temperature control mechanism  14  will be referred to as a measurement unit  10 . 
     The chip cartridge  11  is used with a printed board  22  attached thereto. A base sequence detection chip  21  on which DNA probes are immobilized is mounted on the printed board  22 . 
     In the following embodiments, a DNA base sequence to be detected will be referred to as a target base sequence. A base sequence which is complementary to the target base sequence and selectively reacts with the target base sequence will be referred to as a target complementary base sequence. A DNA probe containing the target complementary base sequence is immobilized to the working electrodes of the base sequence detection chip  21 . A sample (specimen solution) supplied into the cell of the base sequence detection chip  21  contains DNA to be analyzed. The base sequence of the DNA to be analyzed will be referred to as a specimen base sequence. 
     The base sequence detection apparatus according to this embodiment hybridizes the specimen base sequence and target complementary base sequence. After a buffer and an intercalating agent are introduced, the presence/absence of a hybridization reaction is monitored. Accordingly, it can be determined whether the target base sequence is contained in the sample. 
       FIGS. 2A to 2D  are views showing the detailed structure of the chip cartridge  11 .  FIG. 2A  is a plan view.  FIG. 2B  is a view taken along a direction A-A.  FIG. 2C  is a partially perspective sectional view taken along a direction B-B.  FIG. 2D  is a view of a support body  111  as one constituent component of the chip cartridge  11 , which is viewed from the lower surface side. 
     A chip cartridge main body  110  comprises the support body  111  and a chip cartridge top cover  112 . The support body  111  supports the printed board  22  from the lower side. The chip cartridge top cover  112  sandwiches the printed board  22  from the upper side with the support body  111  and fixes and supports the printed board  22 . 
     The chip cartridge top cover  112  has two openings on a side portion. An interface section  113   a  is connected to one of the openings. An interface section  113   b  is connected to the other opening. The interface sections  113   a  and  113   b  function as the interfaces between the solution supply system  13  and the chip cartridge  11 . 
     The interface sections  113   a  and  113   b  have channels  114   a  and  114   b , respectively, inside. A biochemical solution or air from the upstream side of the solution supply system  13  is introduced into the chip cartridge  11  through the channel  114   a . A sample, biochemical solution, or air in the chip cartridge  11  is delivered to the downstream side of the solution supply system  13  through the channel  114   b.    
     Referring to  FIGS. 2A to 2C , the channels  114   a  and  114   b  are indicated by broken lines. The channels  114   a  and  114   b  communicate with the interior of the chip cartridge top cover  112  through the interface sections  113   a  and  113   b  and then communicate with a cell  115 . The cell  115  is a region that is prepared to cause an electrochemical reaction between the base sequence detection chip  21  and various solutions introduced into the base sequence detection chip  21 . When the four corners of the printed board  22  having the base sequence detection chip  21  mounted thereon are fixed to the chip cartridge top cover  112  of the chip cartridge  11  by board fixing screws  25 , the cell  115  is defined as an enclosed spatial region surrounded by the base sequence detection chip  21 , a sealing member  24   a , and the chip cartridge top cover  112 . The printed board  22  having the base sequence detection chip  21  mounted thereon is fixed to the chip cartridge top cover  112 . In this state, the printed board  22  is sandwiched and held by the support body  111  and chip cartridge top cover  112  via the sealing member  24   a . In addition, the chip cartridge top cover  112  is fixed by a top cover fixing screw  117 . Accordingly, the injection/discharge path of various biochemical solutions or air is defined such that it communicates from the channel  114   a  to the channel  114   b  through the cell  115 . The base sequence detection chip  21  is encapsulated to the printed board  22  by an encapsulating resin  23 . 
     The chip cartridge top cover  112  located on the cell  115  has an introduction port  116   a  and a delivery port  116   b . The introduction port  116   a  extends from a side surface to the bottom surface of the chip cartridge top cover  112 . The introduction port  116   a  is open to the bottom surface of the chip cartridge top cover  112  at a cell hole portion  115   a . The delivery port  116   b  extends from another side surface to the bottom surface of the chip cartridge top cover  112 . The delivery port  116   b  is open to the bottom surface of the chip cartridge top cover  112  at a cell hole portion  115   b . The introduction port  116   a  is connected to the channel  114   a . The delivery port  116   b  is connected to the channel  114   b . With this structure, the channel  114   a  and cell  115  communicate with each other while the channel  114   b  and cell  115  communicate with each other. 
     An electrical connector  22   a  is set on the surface printed board  22  at a position separated from the cell  115 . The electrical connector  22   a  is electrically connected to the lead frame of the board main body of the printed board  22 . The lead frame of the board main body is electrically connected to various kinds of electrodes of the base sequence detection chip  21  through leads or the like. The terminal of the measurement system  12  is connected to the electrical connector  22   a . Accordingly, an electrical signal obtained by the base sequence detection chip  21  can be output to the measurement system  12  through a predetermined terminal provided at a predetermined position of the printed board  22  and also through the electrical connector  22   a.    
     As shown in  FIG. 2D , the support body  111  has a U shape. A cut portion  111   a  is formed at the center of the support body  111 . The cut portion  111   a  is smaller than the printed board  22  and larger than the base sequence detection chip  21 . Accordingly, the temperature control mechanism  14  can be arranged in contact with the base sequence detection chip  21  without intervening the support body  111  while maintaining the support function of the printed board  22  by the support body  111 . Reference numeral  117   a  denotes a threaded hole in which the top cover fixing screw  117  is fixed. 
     As the temperature control mechanism  14  which adjusts the temperature of the base sequence detection chip  21 , for example, a Peltier element is used. This enables temperature control within the range of ±0.5° C. The DNA reaction is generally caused in a temperature range relatively close to the room temperature. Hence, if the temperature is controlled using only a heater, the stability is poor. In addition, since the DNA reaction must be controlled in accordance with a temperature control, an independent cooling mechanism is necessary. However, a Peltier element is optimum because it can execute both heating and cooling by changing the direction of a current. 
       FIG. 3  is a view showing the support body  111  and chip cartridge top cover  112  before they are fixed by the top cover fixing screw  117 . As shown in  FIG. 3 , the four corners of the printed board  22  having the base sequence detection chip  21  mounted thereon are fixed to the chip cartridge top cover  112  by the board fixing screws  25 . The sealing member  24   a  is integrated with the chip cartridge top cover  112 . Hence, the cell  115  surrounded by the sealing member  24   a  and chip cartridge top cover  112  is defined on the base sequence detection chip  21 . In addition, the chip cartridge top cover  112  is fixed to the support body  111  by the top cover fixing screw  117 . The board fixing screws  25  may be fixed either from the lower surface side of the printed board  22  or from the upper surface side. When the printed board  22  is fixed to the chip cartridge top cover  112  in this way, the contact between the base sequence detection chip  21 , the sealing member  24   a , and the chip cartridge top cover  112  can be reliably held. 
       FIG. 4  is a view showing the detailed structure of the printed board  22  on which the base sequence detection chip  21  is mounted. As shown in  FIG. 4 , the base sequence detection chip  21  is encapsulated by the encapsulating resin  23 . Working electrodes  501  are formed on the base sequence detection chip  21 . The working electrodes  501  are arranged one by one along the flowing direction of a biochemical solution and air indicated by the arrow in  FIG. 4 . The flowing direction of a biochemical solution and air is defined by enclosing a space along the direction indicated by the arrow around the working electrodes  501  on the base sequence detection chip  21  by the chip cartridge top cover  112  and sealing member  24   a . The region indicated by the broken line is the region where the sealing member  24   a  is arranged. The plurality of working electrodes  501  are arranged within the region indicated by the broken line. 
     The electrical connector  22   a  is arranged at an end portion of the printed board  22 . The working electrodes  501  of the base sequence detection chip  21  and the electrical connector  22   a  are electrically connected by a lead frame provided on the surface of the printed board  22 . When the signal interface of the measurement system  12  is connected to the electrical connector  22   a , each electrode of the base sequence detection chip  21  and the measurement system  12  can be electrically connected. 
       FIG. 5A  is a sectional view showing the cell  115  shown in  FIG. 2A  and a biochemical solution supply system which communicates with the cell  115 , which are viewed from a direction C-C.  FIG. 5B  is a plan view of a portion near the cell  115 . 
     As shown in  FIG. 5A , a channel-shaped projecting portion  112   a  having a height d 42  is formed on the bottom surface of the chip cartridge top cover  112 . The sealing member  24   a  is printed in advance on the channel-shaped projecting portion  112   a  by, e.g., screen printing so that the channel-shaped projecting portion  112   a  is integrated with the sealing member  24   a . Accordingly, the position of the cell  115  can be defined without aligning the sealing member  24   a  and chip cartridge top cover  112 . The assembly step of the cell  115  is simplified. The sealing member  24   a  is fixed between the channel-shaped projecting portion  112   a  and the base sequence detection chip  21 . With this structure, a closed space is defined between the chip cartridge top cover  112  and the base sequence detection chip  21 . This closed space is the cell  115  serving as a reaction chamber where an electrochemical reaction occurs between a probe and a sample or biochemical solution. The bottom surface of the cell  115  is defined by the base sequence detection chip  21 . The side surfaces of the cell  115  are defined by the side portions of the channel-shaped projecting portion  112   a  and sealing member  24   a  arranged on the chip cartridge  112 . The upper surface of the cell  115  is defined by a portion of the chip cartridge  112 , where the channel-shaped projecting portion  112   a  is not formed. With this structure, a closed space which is enclosed except the cell hole portions  115   a  and  115   b  is defined. The liquid-tightness between the base sequence detection chip  21  and a cover  120  is held. The height of the cell  115  is set to about 0.5 mm. In this example, the height is set to about 0.5 mm. However, the present invention is not limited to this. The height is preferably set within the range of 0.1 mm to 3 mm. 
     The cell  115  has a shape with a long channel  601 , as shown in  FIG. 5B , when viewed from the upper side. Referring to  FIG. 5B , there is provided one channel  601  which has the same path width from the cell hole portion  115   a  on the side of the introduction port  116   a  to the cell hole portion  115   b . The channel  601  comprises detection channels  601   a , port connection channels  601   b  and  601   c , and channel connection channels  601   d.    
     The detection channels  601   a  comprise a plurality of channels in which the working electrodes  501  are arranged. The port connection channel  601   b  connects the detection channel  601   a  closest to the cell hole portion  115   a  to the cell hole portion  115   a . The port connection channel  601   c  connects the detection channel  601   a  closest to the cell hole portion  115   b  to the cell hole portion  15   b . The channel connection channels  601   d  connect the end portions of the detection channels  601   a  adjacent to each other to define the flowing direction of a biochemical solution or air through the plurality of detection channels  601   a  to one direction. Accordingly, a biochemical solution or air that flows to a given detection channel  601   a  flows into the channel connection channel  601   d  and then flows into another detection channel  601   a  adjacent in the same direction. All the channels  601   a  to  601   d  have the same path width and section. The path width is preferably 0.5 mm to 10 mm. 
     Referring to  FIG. 5B , the region indicated by the broken line and having no channel  601  is the region where the channel-shaped projecting portion  112   a  and sealing member  24   a  are arranged so that the base sequence detection chip  21  and sealing member  24   a  come into contact. The region having the channel  601  is the region where the channel-shaped projecting portion  112   a  and sealing member  24   a  are not arranged. 
     The introduction port  116   a  and delivery port  116   b  extend upward from the upper surface of the cell  115  to predetermined heights in a direction almost perpendicular to the cell bottom surface. The channels of the introduction port  116   a  and delivery port  116   b  deflect in directions to separate from each other from the center of the cell  115  and are connected to the channels  114   a  and  114   b , respectively. 
     The delivery port  116   b  extends to a predetermined height in a direction almost perpendicular to the cell bottom surface. The delivery port  116   b  also deflects in a direction to separate from the center of the cell  115 . The delivery port  116   b  is branched into two paths at the deflecting position. One path extends through up to the upper surface of the chip cartridge top cover  112  and communicates with a sample injection port  119 . With this structure, a sample injected from the sample injection port  119  is introduced to the cell  115  through the delivery port  116   b . The central axes of the sample injection port  119  and delivery port  116   b  almost coincide with each other. The diameter of the sample injection port  119  is set to be larger than that of the solution supply port  116   b . In addition, the sample injection port  119  can be closed by the cover  120  arranged near the sample injection port  119 . When a biochemical solution is circulated from the channel  114   a  to the channel  114   b  through the cell  115  without using the sample injection port  119 , the cover  120  prevents the biochemical solution from flowing out from the sample injection port  119 . Hence, the path of the biochemical solution can be ensured. The cover  120  has a sealing member  121 . When the sealing member  121  closes the sample injection port  119 , even a slight leakage of the biochemical solution can be prevented. Although not particularly illustrated in the example shown in  FIG. 5A , the sealing member  121  may deeply enter the path to the sample injection port  119  and completely close that path except the path that connects the delivery port  116   b  to the channel  114   b . In this case, retention of a biochemical solution or air on the side of the sample injection port  119  can be reduced. 
     With the above structure, a biochemical solution can flow in a direction indicated by arrows in  FIG. 5A  sequentially through the channel  114   a , introduction port  116   a , cell  115  (channel  601 ), delivery port  116   b , and channel  114   b . A sample is injected from the sample injection port  119  and introduced into the cell  115  through the delivery port  116   b  in a direction indicated by an arrow. Hence, the sample is injected from the delivery side. The biochemical solution supply flow and the sample injection path are set in reverse directions. With this structure, the sample cleaning efficiency in a cleaning process can be increased. 
       FIG. 5C  is a view showing the optimum positional relationship between the introduction port  116   a , the delivery port  116   b , and the channel  601 . The outer edge of the introduction port  116   a  is in contact with that of the port connection channel  601   b . The outer edge of the delivery port  116   b  is separated from that of the port connection channel  601   c . With this structure, the residue of a biochemical solution or air that readily remains near the port corner of the introduction port  116   a  in introducing the biochemical solution or air can be reduced. In addition, a variation in solution supply speed, which is caused at the port corner of the delivery port  116   b  in delivering the biochemical solution or air can be reduced. Furthermore, residual air can be reduced. 
     As indicated by the broken line in  FIG. 5C , the outer edge of the introduction port  116   a  may overlap the outer edge of the port connection channel  601   b . In this case, the introduction port  116   a  projects from the port connection channel  601   b , and the same effect as described above can be obtained. The positional relationship between introduction port  116   a , the delivery port  116   b , and the channel  601  is not limited to that shown in  FIG. 5C , as a matter of course. Three connection forms are available as for the port connection channel  601   b  on the side of the introduction port  116   a : the outer edges overlap or are separated. Three connection forms are available as for the port connection channel  601   c  on the side of the delivery port  116   b : the outer edges are in contact, overlap, or are separated. 
       FIG. 6A  shows a modification of the part indicated by the broken line in  FIG. 5A .  FIG. 6B  is a view showing the cell  115  in  FIG. 6A  when viewed from the upper side. As shown in  FIG. 6A , the introduction port  116   a  has a spot facing hole  115   d . That is, the diameter of the introduction port  116   a  becomes large stepwise toward the spot facing hole  115   d . The diameter of the introduction port  116   a  at a position separated from the opening is smaller than the diameter of the spot facing hole  115   d .  FIG. 6B  shows the positional relationship between them when viewed from the upper side. The spot facing hole  115   d  has a diameter d 11  larger than a diameter d 1  of the introduction port  116   a . The outer edge of the introduction port  116   a  almost coincides with the inner wall of the channel  601 . Hence, part of the outer edge of the spot facing hole  115   d  projects from the region of the cell  115 . The outer edge of the spot facing hole  115   d  need not have a circular shape. For example, as shown in  FIG. 6B , the hole width in a direction parallel to a line  115   c  may be set to be smaller than the hole width in a direction perpendicular to the line  115   c.    
       FIGS. 6A and 6B  show a case wherein the spot facing hole  115   d  is formed at the introduction port  116   a . However, a similar spot facing hole may also be formed at the delivery port  116   b.    
     As described above, when the spot facing hole  115   d  is formed at the opening of the cell  115 , the inlet to the cell  115  has a funnel shape. This provides an effect that a biochemical solution or bubbles can easily be drawn and hardly remain in the cell  115 . 
       FIGS. 7A ,  7 B and  8  are views showing the detailed structure of the cell  115 .  FIG. 7A  is a sectional view taken along a line that connects the cell hole portions  115   a  and  115   b .  FIG. 7B  is a view showing a situation wherein the chip cartridge top cover  112  is being fixed to the base sequence detection chip  21 .  FIG. 8  is the plan view of the cell  115 . 
     As shown in  FIG. 7A , the plurality of detection channels  601   a  are formed at almost equal intervals. When a biochemical solution or air flows from the inside toward this side of the paper through the section of the detection channel  601   a  on the left side of  FIG. 7A , the biochemical solution or air flows in a reverse direction, i.e., away from this side toward the inside of the paper through the detection channel  601   a  at the center. The biochemical solution or air flows again in a reverse direction, i.e., from the inside toward this side of the paper through the detection channel  601   a  on the left side. As described above, the flowing direction of a biochemical solution or air in the adjacent detection channel  601   a  is reversed. 
     When the detection channels  601   a  are cut along a section perpendicular to the flowing direction of a biochemical solution or air, all the detection channels  601   a  have the same rectangular sectional shape. The electrode layouts are also the same. 
     The bottom surface of each detection channel  601   a  is defined by the base sequence detection chip  21 . One working electrode  501  is formed on the bottom surface of each detection channel  601   a.    
     The side surfaces of each detection channel  601   a  are defined by the channel-shaped projecting portion  112   a  projecting from the chip cartridge top cover  112  and the sealing member  24   a . A reference electrode  503  is fixed on each channel side surface, i.e., on a side portion of the channel-shaped projecting portion  112   a  at a predetermined height from the channel bottom surface. The plurality of reference electrodes  503  are located on a plane which is parallel to the chip surface and oppose the chip surface. The plane is located at a position higher than the plane with the working electrodes  501 . 
     The upper surface of each detection channel  601   a  is defined by the bottom surface of the chip cartridge top cover  112  where the channel-shaped projecting portion  112   a  is not formed. A counter electrode  502  is fixed on each channel upper surface. The plurality of counter electrodes  502  are located on planes which are parallel to the chip surface and oppose the chip surface. The planes are located at positions higher than the planes with the working electrodes  502  and reference electrodes  503 . 
     As described above, the working electrodes  501 , counter electrodes  502 , and reference electrodes  503  are three-dimensionally arranged on different planes. 
     The sealing member  24   a  is fixed on the channel-shaped projecting portion  112   a  of the chip cartridge top cover  112  in advance by printing. Hence, when the cell  115  is to be assembled, the chip cartridge top cover  112  integrated with the sealing member  24   a  is pressed against the base sequence detection chip  21  in a direction indicated by the arrows shown in  FIG. 7B . Accordingly, the enclosed channel  601  as shown in  FIG. 7A  is defined between the channel-shaped projecting portion  112   a  and the base sequence detection chip  21  via the sealing member  24   a.    
     As shown in  FIG. 8 , 3-electrodes each comprising the working electrode  501 , counter electrode  502 , and reference electrode  503  are arranged in each detection channel  601   a  at equal intervals along the flowing direction of a biochemical solution or air. The 3-electrodes are arranged on planes perpendicular to the flowing direction of a biochemical solution or air. 
     In the example shown in  FIG. 8 , the working electrodes  501 , counter electrodes  502 , and reference electrodes  503  have a matrix layout independently of the direction of the channel when viewed from the upper side. However, the present invention is not limited to this. As shown in  FIG. 9 , the direction of the channel section structure may be reversed between the adjacent detection channels  601   a  along the flowing direction of a biochemical solution or air. In this case, in all the detection channels  601   a , the counter electrodes  502  are arranged on the right side surfaces of the channels along the flowing direction. Accordingly, 3-electrode layouts can be realized, which have the same shape along the flowing direction of a biochemical solution or air. If the working electrodes  501  and counter electrodes  502  are not laid out symmetrically in the channel sections, they can be laid out such that the layout direction is reversed between the channel sections of the adjacent detection channels  601   a , like the reference electrodes  503 . 
     As described above, sets of three electrodes comprising one working electrode  501 , one counter electrode  502 , and one reference electrode  503  are arranged in the channels having the same shape along the flowing direction of a biochemical solution or air. The 3-electrodes have the same positional relationship. The channel shapes are also the same. When viewed from the working electrode  501 , the distances from the working electrode  501  to the channel bottom surface, side surface, and upper surface and the positional relationship with respect to the counter electrode  502  and reference electrode  503  corresponding to the working electrode  501  are the same for all the working electrodes  501 . Accordingly, the uniformity of the electrochemical signal characteristic detected by each 3-electrode increases. As a result, the detection reliability increases. 
     In this example, the counter electrode  502  and reference electrode  503  are laid out separately from the corresponding working electrode  501 . However, the present invention is not limited to this. The plurality of counter electrodes  502  or reference electrodes  503 , or both of them may be connected. In that case, a region of each electrode, which is closest to a corresponding working electrode, functions as a counter electrode or reference electrode. 
     The sectional shape of the channel is not limited to the structure shown in  FIG. 7A .  FIG. 10  shows a modification of the sectional shape of the channel. 
     As shown in  FIG. 10 , a detection channel  601   e  has the base sequence detection chip  21  as a channel bottom surface. The side surfaces of the channel are defined by the side surfaces of the channel-shaped projecting portion  112   a . The path width of the detection channel  601   e  becomes small upward from the channel bottom surface. The path width is zero at the top portion at the highest position. That is, the boundaries between the channel upper surface or the cell upper surface and the channel side surfaces or the cell side surfaces are not clearly defined. The counter electrode  502  is fixed near the channel top portion. The reference electrode  503  is fixed on a channel-shaped projecting portion  112   c  on the channel side surface, i.e., a plane located between the plane having the counter electrode  502  and the plane having the working electrode  501 . Even in this channel sectional shape, the positional relationship between the three electrodes is the same as in  FIG. 7A . The structure of the remaining parts is the same as in  FIG. 7A , and a detailed description thereof will be omitted. 
       FIG. 11  shows another modification of the sectional shape of the channel. As shown in  FIG. 11 , the structure of the chip cartridge top cover  112  is the same as in  FIG. 7A , including the structure of the channel-shaped projecting portion  112   a . The structure shown in  FIG. 11  is different from that shown in  FIG. 7A  in the layout of the reference electrode  503 . In the example shown in  FIG. 10 , the reference electrode  503  is laid out side by side with the counter electrode  502  on the channel upper surface, i.e., the chip cartridge top cover  112 . In this way, the counter electrode  502  and reference electrode  503  may be formed on the same plane. 
       FIG. 12  is a plan view showing a modification of the detection channel  601   a . In the example shown in  FIG. 12 , the working electrode  501 , counter electrode  502 , and reference electrode  503  are not arranged on the same channel section. Instead, they are arranged at sectional positions shifted from each other in the flowing direction of a biochemical solution or air. In addition, the plurality of counter electrodes  502  are connected by a wiring line  502   a . The plurality of reference electrodes  503  are connected by a wiring line  503   a . The working electrode  501 , counter electrode  502 , and reference electrode  503  are periodically arranged at equal intervals. However, the section on which the counter electrode  502  is formed does not overlap the section on which the reference electrode  503 . The sections are arranged alternately along the flowing direction of a biochemical solution or air. When viewed from the upper side, the working electrode  501  and counter electrode  502  partially overlap. The reference electrode  503  and counter electrode  502  partially overlap. 
     As compared to the case wherein the counter electrode  502  and reference electrode  503  are laid out on the same section, the counter electrode  502  and reference electrode  503  can be arranged in a smaller region. As a result, the channel section can be made small, and the amount of a biochemical solution to be used can be saved. 
     Each counter electrode  502  is connected to the wiring line  502   a . When the wiring line  502   a  is held at a predetermined potential, the plurality of counter electrodes  502  are held at the same voltage. Similarly, each reference electrode  503  is connected to the wiring line  503   a . When the wiring line  503   a  is held at a predetermined potential, the plurality of reference electrodes  503  are held at the same voltage. 
     In the above example, the number of working electrodes  501 , the number of counter electrodes  502 , and the number of reference electrodes  503  equal. However, the numbers need not equal. In addition, the working electrode  501 , reference electrode  503 , and counter electrode  502  need not arranged at sectional positions shifted from each other. The electrodes need not be periodically arranged at equal intervals. 
       FIG. 13A  is a view showing a modification of the structure that defines the channel. The chip cartridge top cover  112  shown in  FIG. 12A  has a flat bottom surface and no channel-shaped projecting portion. A sealing member  24   b  is formed to be thicker than the sealing member  24   a . The sealing member  24   b  is not fixed to the chip cartridge top cover  112  in advance. 
     Hence, as shown in  FIG. 13B , the chip cartridge top cover  112  is not fixed to the base sequence detection chip  21 . In assembling the cell, the sealing member  24   b  is mounted on the base sequence detection chip  21 . The sealing member  24   b  is sandwiched and fixed between the chip cartridge top cover  112  and the base sequence detection chip  21 . With this structure, the enclosed space that surrounds the working electrodes  501 , counter electrodes  502 , and reference electrodes  503  is defined. This enclosed space is the channel  601 . The counter electrodes  502  and reference electrodes  503  are laid out side by side on the bottom surface of the chip cartridge top cover  112 . That is, the counter electrodes  502  and reference electrodes  503  are laid out on the same plane. In the cell  115  shown in  FIGS. 13A and 13B , the cell bottom surface is defined by the base sequence detection chip  21 . The cell side surfaces are defined by only the sealing member  24   b . The cell upper surface is defined by the bottom surface of the chip cartridge top cover  112 . 
       FIG. 14  is a view showing an example of the structure of the sealing member  24   b . As shown in  FIG. 14 , the circular sealing member  24   b  has a channel-shaped hollow portion which extends from the upper surface side to the lower surface side along the shape of the channel  601 . The sidewalls of the hollow portion function as channel walls. In the example shown in  FIGS. 5A to 5C , the channel-shaped projecting portion  112   a  and sealing member  24   a , which defines the channel, have circular outer shapes. However, any other outer shape can be used as long as the channel  601  can be defined. For example, the outer shape may be rectangular, as shown in  FIG. 14 . 
       FIG. 34  is a view showing another modification of the structure that defines the channel shown in  FIG. 13A . In the example shown in  FIG. 13A , each working electrode  501  is arranged on each section perpendicular to the flowing direction of a biochemical solution or cell so that the working electrodes  501  are one-dimensionally laid out along the channel. In the example shown in  FIG. 34 , however, two working electrodes  501  are arranged on each section perpendicular to the flowing direction of a biochemical solution or cell. That is, the working electrodes  501  are two-dimensionally laid out along the channel. In this manner, a predetermined number of working electrodes  501  may be arranged along the channel. In this case, each of the plurality of working electrodes  501  at the same sectional position makes a set with each of the counter electrode  502  and reference electrode  503  located at the section so that they function as a 3-electrode of a potentiostat. 
     A method of manufacturing the above-described base sequence detection chip  21  and printed board  22  will be described next with reference to the sectional views shown in  FIGS. 15A to 15D . 
     A silicon substrate  211  is cleaned. After that, the silicon substrate  211  is heated to form a thermal oxide film  212  on the surface of the silicon substrate  211 . A glass substrate may be used in place of the silicon substrate  211 . 
     A Ti film  213  having a thickness of, e.g., 50 nm and then an Au film  214  having a thickness of, e.g., 200 nm are formed on the entire substrate surface by sputtering. The of the Au film  214  is preferably &lt;111&gt; orientation. A photoresist film  210  is patterned such that regions serving as prospective electrodes and wiring lines are protected ( FIG. 15A ). The Au film  214  and Ti film  213  are etched ( FIG. 15B ). In this embodiment, a KI/I 2  solution mixture is used to etch the Au film  214 . An NH 4 OH/H 2 O 2  solution mixture is used to etch Ti. To etch the Au film  214 , diluted aqua regia may be used. Alternatively, the Au film  214  may be removed by ion milling. The Ti film  213  may also be wet-etched using hydrofluoric acid or buffered hydrofluoric acid. Alternatively, dry etching using a plasma by, e.g., a CF 4 /O 2  mixed gas can also be applied. 
     Next, the photoresist film  210  is removed by oxygen ashing ( FIG. 15C ). The removal process of the photoresist film  210  may be executed using a solvent or a resist stripper. Alternatively, these methods and the oxygen ashing process may be combined. 
     A photoresist  215  is applied to the entire surface and patterned to form openings corresponding to electrode portions and bonding pads ( FIG. 15D ). After that, the resultant structure is hard-baked in a clean oven at, e.g., 200° C. for 30 min. Hard baking may be executed using a hotplate. The processing conditions may also be appropriately changed. 
     In this example, the photoresist  215  is selected as a protective film. However, the present invention is not limited to this. Instead of a photoresist, an organic film made of polyimide or BCB (benzocyclobutene) may be used as a protective film. 
     Alternatively, an inorganic film of SiO, SiO 2 , or SiN may be used as a protective film. For example, when SiO is used, openings are formed in the photoresist such that electrode portions are protected. Then, SiO is deposited. Regions except the electrode portions are protected by lift-off. For example, if SiN is used, SiN is formed on the entire surface. After that, the photoresist  215  is formed and patterned such that openings are formed in correspondence with only electrode portions. Then, the SiN film on the electrodes is removed. Finally, the photoresist  215  is removed. 
     Chips are formed by executing dicing. Finally, to clean the electrode portion surface, a process by a CF 4 /O 2  plasma mixture is executed. With these processes, the base sequence detection chip  21  is obtained. The base sequence detection chip  21  is mounted on the printed board  22  to which the electrical connector  22   a  is attached. The bonding pads of the base sequence detection chip  21  are connected to lead wires on the printed board  22  by wire bonding. After that, the wire bonding portion is protected using the encapsulating resin  23 . 
     With the above process, the printed board  22  having the base sequence detection chip  21  mounted thereon can be manufactured. 
       FIG. 16  is a plan view of the resultant base sequence detection chip  21 . As shown in  FIG. 16 , the plurality of working electrodes  501  are arranged near the center of the chip surface. The region where the working electrodes  501  are formed is smaller than the formation region of the sealing member  24   a , which is indicated by a broken line. Bonding pads  221  are laid out around the chip peripheral portion. Each of the working electrodes  501  is connected to a corresponding one of the bonding pads  221  by a wire  222 . Although not illustrated, the peripheral portion where the bonding pads  221  are formed is encapsulated by the above-described encapsulating resin  23 . 
     A detailed arrangement of the solution supply system  13  will be described next with reference to  FIG. 17 . The solution supply system  13  is roughly divided into a supply system arranged on the side of the channel  114   a  of the chip cartridge  11  and a discharge system arranged on the side of the channel  114   b.    
     An air supply source  401  is connected to the most upstream portion of a pipe  404 . A check valve  402  is arranged downstream of the air supply source  401 . The check valve  402  prevents a biochemical solution except air from flowing back to the air supply source  401  through the pipe  404 . A two-way solenoid valve  403  (V a ) is arranged downstream of the check valve  402 . The two-way solenoid valve  403  controls the flow rate of air from the pipe  404  to the chip cartridge  11 . 
     A milli-Q water supply source  411  which stores milli-Q water as one of biochemical solutions is connected to a pipe  414 . A check valve  412  is arranged downstream of the milli-Q water supply source  411 . The check valve  412  prevents a biochemical solution except the milli-Q water or air from flowing back to the milli-Q water supply source  411 . A three-way solenoid valve  413  (V wa ) is arranged downstream of the check valve  412 . The three-way solenoid valve  413  switches between communication of the pipe  404  and a pipe  415  and communication of the pipe  414  and pipe  415 . More specifically, when the three-way solenoid valve  413  is not electrically turned on, the pipe  404  communicates with the pipe  415 . When the three-way solenoid valve  413  is electrically turned on, the pipe  414  communicates with the pipe  415 . Accordingly, supply of air and supply of milli-Q water to the pipe  415  can be switched. 
     A buffer supply source  421  which stores a buffer (buffer solution) as one of biochemical solutions is connected to a pipe  424 . A check valve  422  is arranged downstream of the buffer supply source  421 . The check valve  422  prevents a biochemical solution except the buffer or air from flowing back to the buffer supply source  421 . A three-way solenoid valve  423  (V ba ) is arranged downstream of the check valve  422 . The three-way solenoid valve  423  switches between communication of the pipe  424  and a pipe  425  and communication of the pipe  415  and pipe  425 . More specifically, when the three-way solenoid valve  423  is not electrically turned on, the pipe  415  communicates with the pipe  425 . When the three-way solenoid valve  423  is electrically turned on, the pipe  424  communicates with the pipe  425 . Accordingly, supply of buffer and supply of air or milli-Q water to the pipe  425  can be switched. 
     An intercalating agent supply source  431  which stores an intercalating agent as one of biochemical solutions is connected to a pipe  434 . A check valve  432  is arranged downstream of the intercalating agent supply source  431 . The check valve  432  prevents a biochemical solution except the intercalating agent or air from flowing back to the intercalating agent supply source  431 . A three-way solenoid valve  433  (V in ) is arranged downstream of the check valve  432 . The three-way solenoid valve  433  switches between communication of the pipe  434  and a pipe  435  and communication of the pipe  425  and pipe  435 . More specifically, when the three-way solenoid valve  433  is not electrically turned on, the pipe  425  communicates with the pipe  435 . When the three-way solenoid valve  433  is electrically turned on, the pipe  434  communicates with the pipe  435 . Accordingly, supply of buffer and supply of air, milli-Q water, or buffer to the pipe  435  can be switched. 
     As described above, in the supply system of air or a biochemical solution, the two-way solenoid valve  403  and three-way solenoid valves  413 ,  423 , and  433  are controlled. With this operation, supply of air and supply of a biochemical solution such as milli-Q water, a buffer, or an intercalating agent, which is to be supplied to the chip cartridge  11  through the pipe  435 , can be switched. In addition, the flow rate of air or a biochemical solution to be supplied can be controlled. 
     The above-described three-way solenoid valve  433  communicates with the upstream side of the pipe  435 . A three-way solenoid valve  441  (V cbin ) communicates with the downstream side of the pipe  435 . With the three-way solenoid valve  441 , the pipe  435  can be branched to a pipe  440  and bypass pipe  446 . When the three-way solenoid valve  441  is not electrically turned on, the pipe  435  communicates with the bypass pipe  446 . When the three-way solenoid valve  441  is electrically turned on, the pipe  435  communicates with the pipe  440 . When a three-way solenoid valve  445  is not electrically turned on, the bypass pipe  446  communicates with a pipe  450 . When the three-way solenoid valve  445  is electrically turned on, the pipe  440  communicates with the pipe  450 . With the three-way solenoid valves  441  and  445 , supply of various kinds of biochemical solutions or air can be switched to the bypass pipe  446  or pipe  440 . 
     A two-way solenoid valve  442  (V 1in ), the chip cartridge  11 , a liquid sensor  443 , a two-way solenoid valve  444  (V 1out ), and the three-way solenoid valve  445  (V cbout ) are arranged downstream sequentially from the three-way solenoid valve  441 . The channel  114   a  corresponding to the introduction system of the chip cartridge  11  communicates with the two-way solenoid valve  442 . The channel  114   b  corresponding to the delivery system of the chip cartridge  11  communicates with the two-way solenoid valve  444 . Accordingly, a biochemical solution or air can be supplied to the introduction system of the chip cartridge  11  through the pipe  440 . In addition, the biochemical solution or air can be delivered from the delivery system of the chip cartridge  11 . The two-way solenoid valves  442  and  444  control the flow rate of a biochemical solution or air in the solution supply and discharge paths. In addition, the liquid sensor  443  can monitor the flow rate of a biochemical solution which enters the chip cartridge  11  or is discharged from the chip cartridge  11 . 
     A two-way solenoid valve  451  (V vin ), a decompression region  452 , a two-way solenoid vale  453  (V out ), a solution supply pump  454 , and a three-way solenoid valve  455  (V ww ) are arranged downstream sequentially from the three-way solenoid valve  445 . The two-way solenoid valves  451  and  453  prevent backflow of a biochemical solution or air in the paths before and after the decompression region  452 . The solution supply pump  454  comprises a tube pump. As a characteristic feature, the solution supply pump  454  is arranged in the discharge system on the delivery side (downstream side) of the chip cartridge  11 . More specifically, when the tube pump is used, the biochemical solution does not come into contact with mechanisms except the tube wall. This structure is preferable from the viewpoint of preventing contamination. Supply/discharge of a biochemical solution or air to/from the chip cartridge  11  is executed by a suction operation. With this operation, a biochemical solution and air can smoothly replace in the chip cartridge  11 . Even if the pipes slack or the chip cartridge  11  is detached from the pipe  440 , no solution leakage occurs. As a result, the safety of apparatus installation increases. 
     The pump may be arranged on a pipe upstream of the chip cartridge  11 . Air or a biochemical solution may be supplied to the chip cartridge  11  by the pump. The pump is not limited to a tube pump. A syringe pump, plunger pump, diaphragm pump, or magnet pump may be used. 
     When the three-way solenoid valve  455  is not electrically turned on, the pipe  450  communicates with a pipe  461 . When the three-way solenoid valve  455  is electrically turned on, the pipe  450  communicates with a pipe  463 . The pipe  461  has a waste liquid tank  462 . The pipe  463  has a waste intercalating agent tank  464 . By switching the three-way solenoid valve  455 , a biochemical solution such as milli-Q water or a buffer except an intercalating agent can be fed to the waste liquid tank  462 , or an intercalating agent can be fed to the waste intercalating agent tank  464 . Accordingly, the intercalating agent can be separately collected. 
     The solenoid valves may be connected by pipes such as Teflon tubes. In this embodiment, manifold structures are formed on both of the upstream and downstream sides of the chip cartridge  11  so that the solenoid valves and channels have integral structures. With this structure, the capacity in the pipes decreases. Hence, the necessary amount of a biochemical solution can greatly be reduced. In addition, the biochemical solution flow in the pipes stabilizes. Hence, the reproducibility and stability of the detection result increase. 
     A solution supply step for base sequence detection using the solution supply system  13  shown in  FIG. 17  will be described with reference to the flow chart shown in  FIG. 18 . 
     First, a hybridization reaction between a sample and DNA probes immobilized to the working electrode  501  is executed in the cell  115  (s 21 ). In executing the hybridization reaction, the temperature control mechanism  14  is controlled such that, e.g., the bottom surface of the chip cartridge  11 , i.e., the bottom surface of the printed board  22  becomes about 45° C. This temperature is held for, e.g., 60 min. 
     In parallel to this hybridization reaction, the biochemical solution line is set up (s 22 ). More specifically, by controlling, the three-way solenoid valves  441  and  445 , the structure on the side of the bypass pipe  446  is used. The three-way solenoid valve  433  is electrically turned on to supply an intercalating agent from the intercalating agent supply source  431  for about 10 sec. The three-way solenoid valve  455  is electrically turned on to store the intercalating agent from the pipe  450  in the waste intercalating agent tank  464 . The intercalating agent and air are alternately repeatedly introduced from the pipe  435  to the bypass pipe  446  for, e.g., about 5 sec each. Next, only air is introduced from the pipe  435  to the bypass pipe  446 . At this time, the waste liquid is switched to the waste liquid tank  462 . A buffer is introduced from the buffer supply source  421  to the bypass pipe  446 . After that, milli-Q water and air are alternately repeatedly introduced from the pipe  435  to the bypass pipe  446  for, e.g., about 5 sec each. 
     When the biochemical solution line is set up, and the hybridization reaction is ended, pipe cleaning is executed (s 23 ). In pipe cleaning, for example, the temperature of the printed board  22  is set to about 25° C. by the temperature control mechanism  14 . The bypass pipe  446  is purged with milli-Q water. Then, air and milli-Q water are alternately repeatedly introduced for, e.g., about 5 sec each. Next, the chip cartridge is cleaned (s 24 ). In chip cartridge cleaning, the biochemical solution introduction path is switched from the bypass pipe  446  to the pipe  440 . Air and milli-Q water are alternately repeatedly introduced to the pipe  440  for, e.g., about 5 sec each. After it is confirmed by the liquid sensor  443  that the chip cartridge  11  is filled with water, the introduction path is switched to the bypass pipe  446 . 
     Next, pipe buffer purge is executed (s 25 ). In pipe buffer purge, first, air is introduced to the bypass pipe  446  such that the buffer and milli-Q water do not mix. Next, air and the buffer are alternately repeatedly introduced to the bypass pipe  446  for, e.g., about 5 sec each. It is confirmed by a liquid sensor  447  arranged on the bypass pipe  446  that the bypass pipe  446  is replaced with the buffer. 
     Next, chip cartridge buffer injection is executed (s 26 ). In chip cartridge buffer injection, first, the bypass pipe  446  is switched to the pipe  440 . Air and the buffer are alternately repeatedly introduced into the chip cartridge  11  for, e.g., about 5 sec each. 
     Then, buffer filling into the chip cartridge  11  is executed (s 27 ). In buffer filling, the buffer is introduced into the chip cartridge  11  while monitoring the state in the chip cartridge  11  with the liquid sensor  443 . The chip cartridge  11  is left to stand at, e.g., 60° C. for 30 min. With this process, the unnecessary sample is cleaned (s 28 ). After the unnecessary sample cleaning step, the pipe  440  is switched to the bypass pipe  446 , and milli-Q water is introduced. Thus, pipe cleaning is executed (s 29 ). In pipe cleaning, air and milli-Q water are alternately repeatedly introduced again for, e.g., about 5 sec each. 
     Next, chip cartridge cleaning is executed (s 30 ). In chip cartridge cleaning, the bypass pipe  446  is switched to the chip cartridge  11 . Air and water are alternately repeatedly introduced for, e.g., about 5 sec each. After it is confirmed by the liquid sensor  443  that the chip cartridge  11  is filled with milli-Q water, the introduction path is switched to the bypass pipe  446 . 
     Next, measurement starts. In the measurement, pipe intercalating agent purge is executed first (s 31 ). In pipe intercalating agent purge, the waste liquid is switched to the waste intercalating agent tank  464  while introducing air to the bypass pipe  446 . Next, air and the intercalating agent are alternately repeatedly introduced to the bypass pipe  446  for, e.g., about 5 sec each. After that, it is detected by the liquid sensor  447  whether the bypass pipe  446  is replaced with the intercalating agent. 
     Next, the intercalating agent is injected into the chip cartridge  11  (s 32 ). In this step, the bypass pipe  446  is switched to the side of the chip cartridge  11 . After that, air and the intercalating agent are alternately repeatedly introduced, e.g., about 5 sec each. 
     Next, under monitoring by the liquid sensor  443 , the chip cartridge  11  is filled with the intercalating agent (s 33 ). Then, measurement is executed (s 34 ). 
     When measurement is ended, milli-Q water is introduced to the bypass pipe  446 . Air and milli-Q water are alternately introduced, e.g., about 5 sec each. The bypass pipe  446  is replaced with air to execute pipe cleaning (s 35 ). 
     Finally, the bypass pipe  446  is replaced to the chip cartridge  11 . Air and milli-Q water are alternately introduced, e.g., about 5 sec each. The chip cartridge  11  is replaced with air to execute chip cartridge cleaning (s 36 ). Thus, the series of solution supply steps are ended. 
     As described above, according to the steps shown in  FIG. 18 , which uses the solution supply system  13  shown in  FIG. 17 , to efficiently replace biochemical solutions, the solutions can be supplied on the basis of a sequence in which air and a biochemical solution alternately flow through the pipe in an order of biochemical solution/air/biochemical solution/air. When this solution supply method is used, mixing of a preceding biochemical solution and a current biochemical solution in biochemical solution replacement can be minimized. As a result, the number of solution exchange transition states decreases. The reproducibility of the final electrochemical characteristic can be increased. In addition, when the efficiency of biochemical solution exchange increases, the solution supply time can be shortened, and the amount of biochemical solution can be decreased. Furthermore, when solution supply is executed on the basis of such a biochemical solution/air sequence, the biochemical solution concentration in the reaction cell  115  can always be kept constant. For this reason, the in-plane uniformity of the current characteristic increases. That is, the detection reliability increases. 
     As a method of filling the cell  115  with a biochemical solution, the two-way solenoid valve  444  serving as a chip cartridge outlet valve is closed. In this state, a decompression state is set in the pipe  440  downstream of the chip cartridge. Then, the two-way solenoid valve  444  is opened. With this method, a biochemical solution can be introduced into the chip cartridge reaction cell  115 . The decompression state in the decompression region  452  is held in the following way. The pump  454  is operated. In this state, the two-way solenoid valve  451  is controlled to reduce the pressure in the decompression region  452 . Then, the two-way solenoid vale  453  is controlled. 
     The solution supply timing shown in  FIG. 18  is merely an example and can be modified in various ways in accordance with the purpose, object, and conditions of measurement. 
       FIG. 19  is a view showing the detailed arrangement of the measurement system  12 . The measurement system  12  shown in  FIG. 19  comprises a 3-electrode potentiostat  12   a . The potentiostat  12   a  feeds back (negative feedback) the voltage of the reference electrode  503  to the input of the counter electrode  502 , thereby applying a desired voltage to a solution independently of the variation in various conditions of the electrodes or solution in the cell  115 . 
     More specifically, the potentiostat  12   a  changes the voltage of the counter electrode  502  to set the voltage of the reference electrode  503  corresponding to the working electrode  501  to a predetermined characteristic. Then, the potentiostat  12   a  electrochemically measures the oxidation current of an intercalating agent. 
     The working electrode  501  is an electrode to which a DNA probe is immobilized. The DNA probe has a target complementary base sequence complementary to a target base sequence. The working electrode  501  is an electrode that detects a reaction current in the cell  115 . The counter electrode  502  is an electrode that applies a predetermined voltage between the counter electrode  502  and the working electrode  501  to supply a current into the cell  115 . The reference electrode  503  is an electrode that feeds back the electrode voltage to the counter electrode  502  to control the voltage between the reference electrode  503  and the working electrode  501  to a predetermined voltage characteristic. By feedback from the reference electrode  503 , the voltage by the counter electrode  502  is controlled. As a result, accurate oxidation current detection can be executed without being influenced by various detection condition in the cell  115 . 
     A voltage pattern generation circuit  510  is connected to the inverting input terminal of an inverting amplifier  512  (OP c ) for reference voltage control of the reference electrode  503  through a wiring line  512   b . The voltage pattern generation circuit  510  generates a voltage pattern to detect the current that flows between the electrodes. 
     The voltage pattern generation circuit  510  converts a digital signal input from the control mechanism  15  into an analog signal to generate a voltage pattern. The voltage pattern generation circuit  510  has a D/A converter. 
     A resistance R s  is connected to the wiring line  512   b . The non-inverting input terminal of the inverting amplifier  512  is grounded. The wiring line  502   a  is connected to the output terminal of the inverting amplifier  512 . The wiring line  512   b  on the inverting input terminal side of the inverting amplifier  512  is connected to the wiring line  502   a  on the output terminal side by a wiring line  512   a . The wiring line  512   a  has a protective circuit  500  formed from a feedback resistance R ff  and a switch SW f . 
     The wiring line  502   a  is connected to a terminal C. The terminal C is connected to the counter electrode  502  on the base sequence detection chip  21 . When a plurality of counter electrodes  502  are formed, the terminal C is connected in parallel with the counter electrodes  502 . Accordingly, a voltage can simultaneously be applied to the plurality of counter electrodes  502  in accordance with one voltage pattern. 
     The wiring line  502   a  has a switch SW 0  which ON/OFF-controls voltage application to the terminal C. 
     The protective circuit  500  arranged in the inverting amplifier  512  prevents any excessive voltage from being applied to the counter electrode  502 . No excessive voltage that electrolyzes a solution is applied at the time of measurement. Oxidation current detection of a desired intercalating agent is not affected. Hence, stable measurement can be executed. 
     A terminal R is connected to the non-inverting input terminal of a voltage follower amplifier  513  (OP r ) by the wiring line  503   a . The inverting input terminal of the voltage follower amplifier is short-circuited, through a wiring line  513   a , to a wiring line  513   b  which is connected to the output terminal of the voltage follower amplifier. The wiring line  513   b  has a resistance R f . The resistance R f  is connected between the resistance of the wiring line  512   b  and the intersection between the wiring lines  512   a  and  512   b . A voltage obtained by feeding back the voltage of the reference electrode  503  to the voltage pattern generated by the voltage pattern generation circuit  510  is input to the inverting amplifier  512 . The voltage of the counter electrode  502  is controlled on the basis of an output obtained by inverting and amplifying these voltages. 
     A terminal W is connected to the inverting input terminal of a trans-impedance amplifier  511  (OP w ) by a wiring line  501   a . The non-inverting input terminal of the trans-impedance amplifier  511  is grounded. A wiring line  511   b  connected to the output terminal is connected to the wiring line  501   a  through a wiring line  511   a . The wiring line  511   a  has a resistance R w . Letting V w  be the voltage of a terminal O on the output side of the trans-impedance amplifier  511 , and I w  be the current, V w =I w ·R w . An electrochemical signal obtained from the terminal O is output to the control mechanism  15 . Since there are a plurality of working electrodes  501 , a plurality of terminals W and a plurality of terminals O are arranged in correspondence with the working electrodes  501 . The outputs from the plurality of terminals O are switched by a signal switching section (to be described later) and A/D-converted so that electrochemical signals from the working electrodes  501  can be almost simultaneously obtained as digital values. The circuits such as the trans-impedance amplifier  511  between the terminal W and the terminal O may be shared by the plurality of working electrodes  501 . In this case, a signal switching section which switches between wiring lines from the plurality of terminals W is arranged in the wiring line  501   a.    
     The effect of the measurement system  12  using the potentiostat  12   a  shown in  FIG. 19  will be described in comparison to the effect obtained using a conventional potentiostat. As shown in  FIG. 20 , the arrangement of a conventional potentiostat  12   a ′ is almost the same as that of the measurement system  12  shown in  FIG. 19 . A difference is that the inverting amplifier  512  has no protective circuit  500 . Let V refin  be the voltage at a terminal I of the voltage pattern generation circuit  510 , V c  be the voltage at the terminal C, and V refout  be the voltage at the terminal R. By feedback of the reference electrode  503 , V refout =R f /R s ·V refin  holds. 
     In this case, examples of the voltage V refin , the switch change-over states of the switches SW 0  and SW f , the voltage characteristics and switch change-over states of the voltages V c  and V refout  are shown in  FIGS. 21A to 21E  and  FIGS. 22A to 22D .  FIGS. 21A to 21E  show waveforms of the potentiostat  12   a .  FIGS. 22A to 22D  show the waveforms of the potentiostat  12   a′.    
       FIG. 21A  shows the voltage waveform of the voltage V refin .  FIG. 21B  shows the switch change-over state of the switch SW 0 .  FIG. 21C  shows the switch change-over state of the switch SW f .  FIG. 21D  shows the voltage waveform of the voltage V c .  FIG. 21E  shows the voltage waveform of the voltage V refout . 
       FIG. 22A  shows the voltage waveform of the voltage V refin .  FIG. 22B  shows the switch change-over state of the switch SW 0 .  FIG. 22C  shows the voltage waveform of the voltage V c .  FIG. 22D  shows the voltage waveform of the voltage V refout . 
     A measuring method in the conventional potentiostat  12   a ′ will be described with reference to  FIGS. 22A to 22D . 
     For example, as shown in  FIG. 22A , the voltage pattern generation circuit  510  generates a voltage pattern which gives a predetermined voltage from times t 1  to t 3  and then linearly decreases and nullifies it at time t 4 . For example, assume a case wherein the switch SW 0  is turned on to apply a voltage to the counter electrode  502  at time t 2  after the elapse of a predetermined time from time t 1 , as shown in  FIG. 22B . In this case, at the start of measurement, i.e., before the switch SW 0  is turned on, the switch SW 0  is OFF. 
     The gain of the inverting amplifier  512  is very large. Hence, if a slight voltage is applied to the inverting input terminal of the inverting amplifier  512  before the switch SW 0  is turned on to form the feedback loop, the output from the inverting amplifier  512  is saturated. On the other hand, even when the voltage V refin  is 0 V, a saturated state is set because of the input offset voltage of the inverting amplifier  512 . In this case, saturation occurs to a polarity opposite to that of the input offset voltage. 
     As described above, the output voltage of the inverting amplifier  512  is saturated almost to the power supply voltage of the inverting amplifier  512 . Hence, when the switch SW 0  is turned on, an excessive voltage is applied to the counter electrode  502 . This excessive voltage corresponds to the hatched portion in  FIG. 22A . The excessive voltage causes an undesirable electrochemical reaction such as electrolysis in a solution in the cell  115 . As a result, measurement of an electrochemical reaction that is originally desired is adversely affected. 
     To solve the problem of the conventional potentiostat  12   a ′, the potentiostat  12   a  of this embodiment uses the protective circuit  500 . In the potentiostat  12   a  of this embodiment, before the start of measurement, i.e., in the initial state before time t a , the voltage V refin  is set to 0 V, the switch SW f  is set in the ON state, and the switch SW 0  is set in the OFF state. First, the switch SW 0  is turned on at time t a . In this state, the switch SW f  is still OFF, and the protective circuit  500  does not function. Since the inverting amplifier  512  is always used with feedback, no excessive voltage is applied to the counter electrode  502 . 
     At time t b  after the elapse of a predetermined time from time t a , the switch SW f  is turned on to cause the protective circuit  500  to function. After that, from time t 1 , the voltage V refin  generated by the voltage pattern generation circuit  510  is applied. With the voltage V refin , a desired voltage is set in the reference electrode  503 . Since the response has a first-order lag characteristic, no excessive voltage is applied to the counter electrode  502 . 
       FIG. 23  is a graph showing current/voltage characteristic curves applied to the counter electrodes  502  in the potentiostats  12   a  and  12   a ′. As shown in  FIG. 23 , in the conventional potentiostat  12   a ′, both the current and the voltage may have large negative values. In the potentiostat  12   a  of this embodiment, however, even when the voltage has a negative value, the current keeps a predetermined value. Conventionally, when the voltage has a negative value, undesirable electrolysis in the solution in the cell  115  progresses. This may, e.g., generate bubbles in the electrodes or change the composition of the electrode. When the protective circuit  500  is used, as in this embodiment, any undesirable voltage can be prevented from being applied to the counter electrode  502 . Hence, any undesirable electrolysis in the solution in the cell  115  can be avoided. As described above, stable measurement can be executed without any adverse effect on oxidation current detection of a desired intercalating agent. 
     Modifications of the potentiostat  12   a  serving as the measurement system  12  shown in  FIG. 19  are shown in  FIGS. 24 to 27 .  FIGS. 24 and 25  show examples in which a 3-electrode potentiostat is used as the measurement system  12 .  FIGS. 26 and 27  show examples in which a 4-electrode potentiostat is used as the measurement system  12 . 
     The basic arrangement of a potentiostat  12   b  shown in  FIG. 24  is the same as that of the potentiostat  12   a  shown in  FIG. 19 . The same reference numerals denote the same parts, and a detailed description thereof will be omitted. The potentiostat  12   b  is different from the potentiostat  12   a  in that the protective circuit  500  is not arranged, including the wiring line  512   a . In place of the protective circuit  500 , a resistance R c  is arranged in the wiring line  502   a . When the resistance R c  is connected in series with the output from the inverting amplifier  512  on the side of the counter electrode  502 , the voltage applied to the counter electrode exhibits a first-order delay due to the double layer capacitance. Accordingly, the influence on the biochemical solution in the cell  115  can be reduced. 
     The arrangement of a potentiostat  12   c  shown in  FIG. 25  is slightly different from those of the potentiostats  12   a  and  12   b . In the potentiostat  12   c , the current detection resistance R c  is arranged on the side of the counter electrode  502 . A detected current is converted into a voltage by a high-input impedance differential amplifier  520 . The arrangement will be described below in more detail. 
     As shown in  FIG. 25 , the voltage pattern generation circuit  510  which generates a voltage pattern to detect a current between the electrodes is connected to the inverting input terminal of the inverting amplifier  512  (OP c ) through the wiring line  512   b . The resistance R s  is connected to the wiring line  512   b . The non-inverting input terminal of the inverting amplifier  512  is grounded. A wiring line  512   f  is connected to the output terminal. The output terminal and inverting input terminal of the inverting amplifier  512  are connected by the protective circuit  500 . 
     The wiring line  512   f  has the switch SW 0  which ON/OFF-controls voltage application to the terminal C. The wiring line  512   f  is branched to two wiring lines  521   a  and  521   b  at an intersection  512   c . The wiring line  521   a  is connected to the non-inverting input terminal of an amplifier  522  in the high-input impedance differential amplifier  520 . 
     The wiring line  521   b  has the current detection resistance R c . The wiring line  521   b  is branched to the wiring line  502   a  and a wiring line  521   e  at an intersection  521   d . The wiring line  502   a  is connected to the terminal C. The wiring line  521   e  is connected to the non-inverting input terminal of an amplifier  523  in the high-input impedance differential amplifier  520 . 
     The arrangement of the voltage follower amplifier  513 , wiring lines  513   a  and  513   b , and resistance R f , which feeds back a voltage from the terminal R on the side of the reference electrode  503  to the inverting input terminal of the inverting amplifier  512 , is the same as in  FIG. 19 . 
     The terminal W on the side of the working electrode  501  is grounded through the wiring line  501   a.    
     The high-input impedance differential amplifier  520  amplifies the differential voltage between the output from the wiring line  521   a  without intervening the current detection resistance R c  and the output from the wiring line  521   e  through the current detection resistance R c  and outputs the differential voltage to the terminal O. The inverting input terminals of the amplifiers  522  and  523  are connected by a wiring line  522   a  having a resistance R 1 . The inverting input terminal and output terminal of the amplifier  522  are connected by a wiring line  522   b  having a resistance R 2 . The inverting input terminal and output terminal of the amplifier  523  are connected by a wiring line  523   a  having a resistance R 3 . The output from the amplifier  522  is connected to the inverting input terminal of an amplifier  524  through a resistance R 4 . The output from the amplifier  523  is connected to the non-inverting input terminal of an amplifier  525  through a resistance R 5 . The amplifier  524  is grounded through a resistance R 6 . The inverting input terminal and output terminal of the amplifier  524  are connected by a wiring line  522   d  having a resistance R 7 . The output terminal of the amplifier  524  is connected to the terminal O by a wiring line  524   b.    
     In the potentiostat  12   c , an oxidation current is detected not from the working electrode  501  but from the counter electrode  502 . 
     As described above, even when the potentiostat  12   c  shown in  FIG. 25  is used, the same effect as that of the potentiostat  12   a  can be obtained. 
     The arrangements on the side of the counter electrode  502  and on the side of the working electrode  501  of a 4-electrode potentiostat  12   d  shown in  FIG. 26  are the same as those of the potentiostat  12   a  shown in  FIG. 19 . In the potentiostat  12   d , the voltages from two reference electrodes  5031  and  5032  are differentially amplified by using the high-input impedance differential amplifier  520 . The differential amplified voltage is fed back to the inverting amplifier  512  on the side of the counter electrode  502 . In this way, the potential difference between the two reference electrodes is detected. The supply current from the counter electrode  502  is controlled such that the value of the potential difference has a predetermined voltage characteristic. 
     As shown in  FIG. 26 , a terminal R 1  on the side of the reference electrode  5031  is connected to the non-inverting input terminal of the amplifier  523 . A terminal R 2  on the side of the reference electrode  5032  is connected to the non-inverting input terminal of the amplifier  522 . The high-input impedance differential amplifier  520  differentially amplifies the two voltage of the non-inverting input terminals of the amplifiers  522  and  523  and outputs the differential voltage. The output side of the high-input impedance differential amplifier  520  is connected to the wiring line  512   b  through the resistance R f . 
     As described above, even when the potentiostat  12   d  shown in  FIG. 26  is used, the same effect as that of the potentiostat  12   a  can be obtained. 
     The basic arrangement of a 4-electrode potentiostat  12   e  shown in  FIG. 27  is the same as that of the potentiostat  12   c  shown in  FIG. 25 . The difference from the potentiostat  12   c  is that the potentiostat  12   e  has two reference electrode extraction voltages, and the two voltages are differentially amplified and fed back to the side of the counter electrode  502 . The arrangements on the side of the counter electrode  502  and on the side of the working electrode  501  are the same as those of the potentiostat  12   c , and a detailed description thereof will be omitted. Reference numeral  520 ′ denotes a high-input impedance differential amplifier that has the same arrangement as the above-described high-input impedance differential amplifier  520 . 
     As shown in  FIG. 27 , in the potentiostat  12   e , the outputs from the terminal R 1  on the side of the reference electrode  5031  and the terminal R 2  on the side of the reference electrode  5032  are respectively connected to the non-inverting input terminal of the amplifier  523  and the non-inverting input terminal of the amplifier  522 . As described above, the high-input impedance differential amplifier  520  differentially amplifies the two inputs and outputs the differential voltage. The resistance R f  is connected to the output side. The high-input impedance differential amplifier  520  is connected to the wiring line  512   b  through the resistance R f . With this structure, the output from the high-input impedance differential amplifier  520  is fed back to the input side of the inverting amplifier  512 . 
       FIG. 28  is a block diagram showing the association between the control mechanism  15  and the remaining constituent elements of the computer  16 . As shown in  FIG. 28 , the computer  16  comprises a main processor  16   a  and an interface  16   b . Data can be transmitted/received to/from the plurality of control mechanisms  15  via the interface  16   b  through a local bus  17 . The control mechanism  15  comprises a measurement control mechanism main body  15   a  and a data memory  15   b  which stores data to be handled by the measurement control mechanism main body  15   a . One control mechanism  15  is arranged in correspondence with each measurement unit  10 . As the plurality of connected measurement units  10  are connected to one main processor  16   a , the load on the main processor  16   a  can be reduced. 
       FIG. 29  is a block diagram showing a detailed arrangement of the control mechanism  15 . As shown in  FIG. 29 , the measurement control mechanism main body  15   a  has an initial value register  151 , step value register  152 , terminal value register  153 , interval register  154 , and operation setting register  155 , which are connected to the local bus  17 . 
     The initial value register  151 , step value register  152 , terminal value register  153 , interval register  154 , and operation setting register  155  store an initial value, step value, terminal value, measurement time interval, and operation mode, respectively, which can be set by the main processor  16   a . When an initial value, step value, terminal value, measurement time interval, and operation mode are set, a data measurement operation is started. 
     The initial value, step value, and terminal value represent a value corresponding to the voltage value of a voltage pattern to be generated by the voltage pattern generation circuit  510 . A voltage pattern is set as a digital value from the initial value to the terminal value for every step value. For example, assume that a voltage pattern having a predetermined waveform is to be generated from times t 1  to t 5 . The voltage value at time t 1  corresponds to the initial value. The voltage value varies by the step value from time t 1  at a measurement time interval Δt. Such a voltage value changes stepwise to the terminal value. 
     Only at the start of measurement, a selector  158  selectively outputs the initial value from the output value from the initial value register and the output value from an adder  156 . From the next data, the selector  158  selectively outputs the sum from the adder  156 . The output value from the selector  158  is output to the voltage pattern generation circuit  510  of the measurement system  12  in synchronism with the output signal from a timing generator  161 . The voltage pattern generation circuit  510  generates a voltage having a voltage value corresponding to the output value from the selector  158 . With this operation, a voltage pattern having the voltage waveform shown in  FIG. 21A  described above can be generated. 
     An adding register  157  temporarily stores the output value from the selector  158  in synchronism with the output signal from the timing generator  161 . 
     The adder  156  adds the step value from the step value register  152  to the initial value from the initial value register  151  and outputs the sum to the selector  158  and a comparator  159 . The value stored in the adding register  157  corresponds to the voltage value to be output to the measurement system  12 . Hence, the adder  156  outputs a value corresponding to a voltage value as the sum of the step value and the output voltage value to the measurement system  12 . The comparator  159  compares the sum from the adder  156  with the terminal value from the terminal value register  153 . When the sum exceeds the terminal value, the comparator  159  outputs a signal representing the end of count to a counter  160 . 
     The counter  160  counts clocks on the basis of the operation setting mode from the operation setting register  155  for a period defined by the measurement time interval from the interval register  154 . The counter  160  continues counting until the count end signal is input from the comparator  159 . 
     As the operation setting mode, a single measurement mode, 4-electrode setting mode, 8-electrode setting mode, or the like can be set in accordance with, e.g., the number of working electrodes to be measured simultaneously. When, e.g., the single measurement mode is set, the counter  160  executes counting for the period defined by the measurement time interval and outputs the count value to the timing generator  161 . When the 4-electrode setting mode is set, the counter  160  executes counting for each of periods obtained by dividing the measurement time interval into four parts and outputs the count value to the timing generator  161 . As described above, when a multiple electrode setting mode is set, counting is executed for each of periods obtained by dividing the measurement time interval into parts equal in number to the electrodes. 
     The timing generator  161  outputs an address signal and write signal to the data memory  15   b  in synchronism with the output timing of the count value from the counter  160  while counting the clocks. The timing generator  161  also switches a signal switching section  163  of a signal detection section  162  in accordance with the operation setting mode from the operation setting register  155 . 
     The signal switching section  163  is connected to the terminals O of the plurality of working electrodes  501  of the measurement system  12 . In the plurality of working electrodes  501 , electrochemical signals by an intercalating agent can be simultaneously detected for the terminals O. With the signal switching section  163 , one of the electrochemical signals from the plurality of working electrodes  501  can selectively be detected. 
     The signal detection section  162  A/D-converts the electrochemical signal from the working electrode  501  switched by the signal switching section  163  controlled by the timing generator  161  and outputs the electrochemical signal to the data memory  15   b  through a data bus  164 . Accordingly, every time a write signal from the timing generator  161  is input, data from the data bus  164  can sequentially be written in the data memory  15   b  at an address position given by each write signal. 
     In, e.g., the single electrode setting mode, when the measurement time interval is 10 msec, a write signal and an address are output from the timing generator  161  to the data memory  15   b  once in a period of 10 msec. In addition, the digital conversion value of an electrochemical signal is output from the signal detection section  162  to the data memory  15   b  through the data bus  15   b.    
     In the 4-electrode setting mode, when the measurement time interval is 10 msec, a write signal and four addresses are output from the timing generator  161  to the data memory  15   b  four times in a period of 10 msec. In addition, the digital conversion values of the four electrochemical signals are sequentially output from the signal detection section  162  to the data memory  15   b  through the data bus  15   b . Accordingly, the electrochemical signals that are almost simultaneously detected at the measurement time interval can be stored as data. 
     To increase the accuracy of measurement, in the multiple electrode setting mode, the signal detection timing from the plurality of working electrodes  501  may be shortened without synchronizing the detection timing with the timing obtained by equally dividing the measurement time interval. For example, when a plurality of switching signals of the signal switching section  163  are generated in a short time in the measurement time interval, a measurement accuracy independently of the measurement time interval can be maintained. For example, when the measurement time interval is 10 msec, no switching signal is generated during initial 9 msec. The timing generator  161  is programmed such that switching signals are generated in 1 msec between the timing corresponding to 9 msec and that corresponding to 10 msec and output to the signal switching section  163 . With this setting, electrochemical signals from the four working electrodes  501  can be detected within 1 msec. Hence, even when a long measurement time interval is set, no variation in measurement time interval is generated, and a high accuracy can be maintained. 
     The measurement data stored in the data memory  15   b  are read out by the main processor  16   a  of the computer  16  and used for various kinds of signal analysis. 
     As described above, when a plurality of measured electrochemical signals are switched and selectively detected at a shorter interval than the measurement time interval set by the timing generator  161 , the signals of the working electrodes  501  can be almost simultaneously measured. 
     One example of a measurement data analyzing method of causing the computer  16  to execute signal analysis on the basis of measurement data will be described next. A type determination analyzing method which determines whether the base at the SNP position of a target DNA is G type (homo type), T-type (homo type), or GT-type (hetero type) will be described here with reference to the flow chart shown in  FIG. 30 . Although not particularly illustrated in  FIG. 1  or  28 , the main processor  16   a  of the computer  16  executes an analysis program comprising a plurality of commands for type determination filtering, type determination processing, and determination result output, thereby executing type determination filtering, type determination processing, and determination result output. In addition, for control of the above-described control mechanism  15 , a control program is separately prepared. The analysis program or control program may be executed by causing a recording medium reading device arranged in the computer  16  to read out the analysis program stored in a recording medium. Alternatively, the program may be read out from a storage device such as a magnetic disk provided in the computer  16  and executed. 
     As a presupposition of measurement data analysis, four types of target base sequences, which have A, G, C, and T as bases at SNP positions, are prepared as objects to be detected. A plurality of target complementary DNA probes, which have base sequences complementary to the target base sequences, are immobilized to the working electrodes  501  in correspondence with the respective types. In addition, a plurality of DNA probes (to be referred to as negative control hereinafter) having base sequences different from those of the four target complementary DNA probes are immobilized to other working electrodes  501  (s 61 ). Note that DNA probes of one kind are fixed to the working electrodes  501  in principle. 
     A sample containing the specimen DNA probe is injected into the base sequence detection chip on which the above-described target complementary DNA probes are fixed. A hybridization reaction is caused (s 62 ). Cleaning by a buffer and an electrochemical reaction by introduction of an intercalating agent are executed. Then, a representative current value is calculated using the measurement system  12  (s 63 ). 
     The representative current value indicates a numerical value that is effective for quantitatively grasping occurrence of hybridization reactions of the respective DNA probes. For example, the maximum value (peak current value) of the current value of a detected signal corresponding to the representative current value. The peak current value is derived by measuring an oxidation current signal from an intercalating agent which is bonded to double stranded DNA hybridized to the DNA probe immobilized to each working electrode  501  and obtaining the peak of the current value. The peak current value is preferably detected by subtracting a background current except the oxidation current signal from the intercalating agent. 
     Any other value may be defined as the representative current value in accordance with the accuracy or object of signal processing. For example, the integral value of oxidation current signals can be used. Not a current value but a voltage value or a value obtained by executing numerical value analysis processing for the current or voltage may be defined as the representative current value. 
     Measurement data, i.e., representative current values related to the target DNA with A, G, C, and T as bases at the SNP positions are defined as X a , X g , X c , and X t . The representative current value of the DNA probe of negative control is defined as X n . A plurality of representative current values are obtained for each type. To identify the representative current values, first X a  is defined as X a1 , second X a  is defined as X a2 , . . . . 
     The numbers of representative current values obtained for the target DNA with A, G, C, and T as bases at the SNP positions are defined as n a , n g , n c , and n t . The number of representative current values obtained for negative control is defined as n n . 
     Next, to remove clearly abnormal data from the obtained representative current values X a , X g , X c , X t , and X n , type determination filtering processing is executed (s 64 ). 
       FIG. 31  is a flow chart of type determination filtering processing. The type determination filtering processing shown in  FIG. 31  is executed for each of X a , X g , X c , X t , and X n . For, e.g., X a , representative current values that are supposed to be clearly abnormal are excluded from the n a  representative current values obtained for X a  by the type determination filtering. The same processing is executed even for X g , X c , X t , and X n . 
     In the description of  FIG. 31 , the same processing is executed in accordance with the data type. Filtering for X a  will be exemplified. 
     More specifically, as shown in  FIG. 31 , all measurement data of each measurement group are set. That is, data sets are set (s 81 ). For, e.g., X a , X a1 , X a2 , . . . , X ana  are set as data sets. 
     Next, a CV value (to be referred to as a value CV 0  hereinafter) for the measurement data X a1 , X a2 , . . . , X ana  is calculated (s 82 ). The value CV 0  is obtained by dividing the standard deviation of the measurement data X a1 , X a2 , . . . , X ana  by the average value. It is determined whether the obtained value CV 0  is 10%, i.e. 0.1 or more (s 83 ). 
     If the value CV 0  is 10% or more, a CV value (to be referred to as a value CV 1  hereinafter) of (na−1) data sets, excluding the minimum value of the measurement data, is calculated (s 84 ). If the value CV 0  is less than 10%, it is determined that no data is clearly abnormal, and the flow advances to type determination (to be described later). 
     After CV 1  is calculated, it is determined whether CV 0 ≧2×CV 1  (s 85 ). When this inequality holds, the flow advances to (s 86 ) to newly define (na−2) data sets, excluding the minimum value of the measurement data. The flow returns to (s 82 ) to repeatedly execute abnormal data filtering. 
     When the inequality does not hold, it is determined that abnormal data is present not on the minimum value side but on the maximum value side. A CV value (to be referred to as a value CV 2  hereinafter) of (na−2) data sets, excluding the maximum value of the measurement data, is calculated (s 87 ). It is determined whether CV 0 ≧2×CV 2  (s 88 ). When this inequality holds, (na−3) data sets, excluding the maximum value of the measurement data, are newly set as data sets. The flow returns to (s 82 ) to repeatedly execute abnormal data filtering. If the inequality does not hold, it is determined that no data is clearly abnormal, and the flow advances to type determination (to be described later). 
     The above-described type determination filtering is executed even for X g , X c , X t , and X n . 
     Next, type determination processing is executed using the obtained type determination filtering result (s 65 ). An example of the type determination processing will be described with reference to the flow chart shown in  FIG. 32 . In the example shown in  FIG. 32 , type determination is performed to determine whether the base at the SNP position of target DNA is G type, T type, or GT type. This type determination processing is roughly divided into a maximum group determination algorithm and a 2-sample t-test algorithm. 
     As shown in  FIG. 32 , first, the average value of the representative current values of each group is extracted (s 91 ). The groups are X a , X g , X c , X t , and X n . That is, DNA probes with different target base sequences are put into different groups, and DNA probes having the same target base sequence are input into the same group. In (s 64 ), measurement data excluding clearly abnormal data are extracted by type determination filtering. Measurement data excluding abnormal data may be extracted by filtering except the type determination filtering in (s 64 ). Measurement data may be extracted without executing any filtering. Instead of the average value of the representative current values, another statistical processing value may be obtained by statistical processing of the statistical values. 
     Groups which have A, G, C, and T as bases at the SNP position of target DNA are defined as groups A to T. A group for negative control is defined as a group N. The obtained average values for the groups X a , X g , X c , X t , and X n  are defined as M a , M g , M c , M t , and M n , respectively. 
     For the obtained average values M a , M g , M c , M t , and M n , it is determined whether the average value M g  of the group G is maximum (s 92 ). If M g  is maximum, the flow advance to (s 93 ). If M g  is not maximum, the flow advances to (s 97 ). 
     In (s 97 ), for the average values M a , M g , M c , M t , and M n , it is determined whether the average value M t  of the group T is maximum. If M t  is maximum, the flow advance to (s 99 ). If M t  is not maximum, neither the groups G and T are maximum. Since determination is impossible, re-inspection is executed. 
     In (s 93 ), it is determined whether a difference is present between the measurement data X g1 , X g2 , . . . of the group G and the measurement data X n1 , X n2 , . . . of the group N. To determine whether a difference is present, for example, 2-sample t-test is used. More specifically, a probability P and a significance level α obtained by 2-sample t-test are compared as the representative relationship. 
     H 0 : when P≧α, no significant difference is present (null hypothesis) 
     H 1 : when P&lt;α, a significant difference is present (alternative hypothesis) 
     The significance level α can be set by the user using the computer  16 . In the example of (s 93 ), a question for H 1 , i.e., whether a difference is present between the measurement data of the group G and that of the group N is raised. For this question, the hypothesis H 1  that no difference is present between the two groups is set. The probability is obtained assuming that the difference between the two groups is summarized in the average value M g  of the group G and the average value M n  of the group N. To calculate the probability, a statistical constant t and a degree of freedom φ are calculated on the basis of the statistical values X g1 , X g2 , . . . of the group G and the statistical values X n1 , X n2 , . . . of the group N. The probability P is obtained from the integral value of the probability density variables of the t-distribution. 
     For the obtained probability P, when P≧α, H 0  cannot be discarded, and determination is retained. That is, it is determined that no difference is present. When P&lt;α, H 0  is discarded, and the hypothesis H 1  is employed. It is determined that a difference is present. 
     When it is determined that “a difference is present”, the flow advances to (s 94 ). When it is determined that “no difference is present”, determination is impossible, and re-inspection is executed. 
     In (s 94 ), for the group G and group A, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the flow advances to (s 95 ). If no difference is present, determination is impossible, and re-inspection is executed. 
     In (s 95 ), for the group G and group C, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the flow advances to (s 96 ). If no difference is present, determination is impossible, and re-inspection is executed. 
     In (s 96 ), for the group G and group T, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the group G type is determined. This is because the group G type has the maximum average value and differences to the remaining measurement groups. If no difference is present, the group GT type is determined. This is because the group G type has the maximum average value though the measurement result of the group G type and that of the group T type have no difference. 
     In (s 98 ), for the group T and group N, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the flow advances to (s 99 ). If no difference is present, determination is impossible, and re-inspection is executed. 
     In (s 99 ), for the group T and group A, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the flow advances to (s 100 ). If no difference is present, determination is impossible, and re-inspection is executed. 
     In (s 100 ), for the group T and group C, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the flow advances to (s 101 ). If no difference is present, determination is impossible, and re-inspection is executed. 
     In (s 101 ), for the group T and group G, it is determined using the same 2-sample t-test as in (s 93 ) whether a difference is present between the two groups. If a difference is present, the group T type is determined. This is because the group T type has the maximum average value and differences to the remaining measurement groups. If no difference is present, the group GT type is determined. This is because the group T type has the maximum average value though the measurement result of the group T type and that of the group G type have no difference. 
     The above determination results are displayed on a display apparatus (not shown) arranged in the computer  16  (s 66 ). When the above type determination algorithm is used, a hetero type can be determined. 
       FIGS. 30 to 32  show a method of determining whether the type corresponds to the G type, T type, or GT type. This method can also be applied to determine two of the A type, G type, C type, and T type or determine a hetero type thereof. In addition, measurement data need not always be acquired for the four types of groups, i.e., A type, G type, C type, and T type. For example, measurement data may be acquired for only two groups related to two considerable bases of SNP. In addition, one group for negative control may be added to the two groups. 
     A base sequence automatic analyzing method using the above-described base sequence detection apparatus will be described with reference to the sequence chart shown in  FIG. 33 . 
     As shown in  FIG. 33 , first, automatic analysis condition parameters for automatic analysis are set by using the computer  16 . The user instructs the computer  16  to execute automatic analysis based on the set automatic analysis condition parameters (s 301 ). The automatic analysis condition parameters are control parameters used to control the control mechanism  15 . The control parameters used in the control mechanism  15  include measurement system control parameters used to control the measurement system  12 , solution supply system control parameters used to control the solution supply system  13 , and temperature control mechanism control parameters used to control the temperature control mechanism  14 . 
     The measurement system control parameters are input setting parameters stored in the above-described initial value register  151 , step value register  152 , terminal value register  153 , interval register  154 , and operation setting register  155  shown in  FIG. 29 . The input setting parameters comprise the initial value, step value, terminal value, measurement time interval, and operation mode. 
     The solution supply system control parameters include solenoid valve control parameters used to control the solenoid valves  403 ,  413 ,  423 ,  433 ,  441 ,  442 ,  444 ,  445 ,  451 ,  453 , and  463 , sensor control parameters used to control the liquid sensors  443  and  447 , and a pump control parameter used to control the pump  454 . The solenoid valve control parameters, sensor control parameters, and pump control parameter more specifically include the control amounts of objects to be controlled, the control timings of objects to be controlled, and control conditions for controlling objects to be controlled as conditions to sequentially execute the series of processes shown in (s 22 ) to (s 36 ) in  FIG. 18 . 
     The temperature control parameters accompany the solution supply system control parameters in principle. More specifically, when the solution supply system control parameters are set, the temperature control parameters are set in correspondence with the operation of the solution supply system  13 . Accordingly, temperature control of the temperature control mechanism  14  can be executed in synchronism with the solution supply system  13 . 
     When automatic analysis is executed, the automatic analysis condition parameters are transmitted to the control mechanism  15  (s 302 ). The control mechanism  15  controls the measurement system  12  on the basis of the measurement system control parameters. The control mechanism  15  controls the solution supply system  13  on the basis of the solution supply system control parameters. The control mechanism  15  controls the temperature control mechanism  14  on the basis of the temperature control mechanism control parameters. The control mechanism  15  also manages the control timings of the measurement system  12 , solution supply system  13 , and temperature control mechanism  14  on the basis of the control timings and control conditions included in the control parameters. Hence, the control sequence is freely defined in accordance with the automatic analysis condition parameters set by the user. In  FIG. 33 , a typical example will be described. 
     Independently from the automatic analysis, the user prepares the chip cartridge  11 . First, desired DNA probes are immobilized to the working electrodes  501  of the base sequence detection chip  21 . The printed board  22  in which the base sequence detection chip  21  is encapsulated is fixed to the support body  111  of the chip cartridge  11  with the board fixing screws  25  and thus attached to the chip cartridge  11  (s 401 ). The chip cartridge top cover  112  having the sealing member  24   a  integrated and the support body  111  are fixed using the top cover fixing screw  117  to form the cell  115 . The chip cartridge  11  in this state is prepared (s 402 ). A sample is injected into the chip cartridge  11  through the sample injection port  119  (s 403 ). When the chip cartridge  11  is attached to the apparatus main body, and a start operation is executed, a hybridization reaction (s 21 ) starts. The amount of the sample injected is preferably slightly larger than the volume of the cell  115 . In this case, the cell  115  can be completely filled with the sample without any remaining air. 
     The control mechanism  15  starts controlling the timing of the measurement system on the basis of the measurement system control parameters received from the computer  16  (s 303 ). 
     The control mechanism  15  also sequentially controls the constituent elements of the solution supply system  13  on the basis of the solution supply system control parameters received from the computer  16  (s 304 ). Although not particularly illustrated in  FIG. 33 , temperature control of the temperature control mechanism  14  is executed on the basis of the temperature control mechanism control parameters in synchronism with the control of the solution supply system  13 . By this control, the solution supply system  13  automatically executes the solution supply step shown in (s 21 ) to (s 36 ) (except s 34 ) in  FIG. 18 , including the hybridization reaction (s 305 ). In addition, the temperature control mechanism  14  is automatically controlled such that the base sequence detection chip  21  is set to the temperature designated in the solution supply step. 
     The control mechanism  15  sends a measurement command to the measurement system  12  in synchronism with the timing of the measurement step (s 34 ) in the solution supply step (s 305 ). More specifically, at the timing of the measurement step (s 34 ) in the solution supply step, the initial value, step value, terminal value, measurement time interval, and operation setting mode are stored in the initial value register  151 , step value register  152 , terminal value register  153 , interval register  154 , and operation setting register  155 . The above-described measurement system timing control (s 303 ) may be executed simultaneously with (s 305 ). 
     The measurement system  12  executes measurement by generating, e.g., a voltage pattern on the basis of the measurement command (s 306 ). The obtained measurement signal is output from the terminal O to the control mechanism  15  (s 307 ). The control mechanism  15  processes the received measurement signal and stores it in the data memory  15   b  as measurement data (s 308 ). The measurement data is output to the computer  16  through the local bus  17  (s 309 ). The computer  16  receives the measurement data (s 310 ). 
     When the necessary measurement data is obtained, the computer  16  executes type determination filtering in (s 64 ) shown in  FIG. 31  on the basis of the measurement data. When type determination filtering is ended, type determination processing shown in  FIG. 32  is executed on the filtered data (s 65 ). Finally, the obtained determination result is displayed on the display apparatus of the computer  16  (s 66 ). 
     As described above, according to this embodiment, a uniform reaction environment is obtained for the 3-electrode system comprising a working electrode, counter electrode, and reference electrode. For this reason, the flow velocity of a biochemical solution is constant on the electrodes. The uniformity of the electrochemical reaction in the channels increases. As a result, the reliability of the detection result increases. In addition, when the counter electrode and reference electrode are arranged on planes different from that of the working electrode, the layout density of the working electrodes can be increased. Furthermore, when DNA probes are to be immobilized to the working electrodes  501 , the counter electrode  502  or reference electrode  503  is not contaminated. 
     In addition, after the specimen DNA solution is injected into the chip cartridge  11 , the whole process from hybridization to cleaning of nonspecific absorption DNA by a buffer, injection of an intercalating agent, electrochemical measurement, storage of measurement data, and determination of target base sequence based on the measurement data can be automatically executed. Accordingly, the detection signal reproducibility and the detection accuracy can be increased, and the time until result derivation can be shortened. 
     The present invention is not limited to the above embodiment. 
     The probe immobilized to the working electrode  501  is a DNA probe in the above embodiment. However, a probe formed from any other nucleic acid except DNA may be used. In addition, any other probe that is not formed from a nucleic acid and has a predetermined base sequence may be used. 
     The process assignment to the computer  16  and control mechanism  15  is not limited to the above-described example. For example, when each of the measurement system  12 , solution supply system  13 , and temperature control mechanism  14  has a processor which interprets a command from the computer  16  and executes each constituent element, the control mechanism  15  may be omitted. In this case, the function of the control mechanism  15  shown in  FIG. 29  is executed by the computer  16 . 
     As for management of timings of the measurement system  12 , solution supply system  13 , and temperature control mechanism  14 , when each of the measurement system  12 , solution supply system  13 , and temperature control mechanism  14  has a processor which manages the timing, each process is executed on the basis of the timing managed by the processor. In this case, the computer  16  only needs to transmit automatic analysis condition parameters to the measurement system  12 , solution supply system  13 , and temperature control mechanism  14  and need not manage the timings. 
     Alternatively, the computer  16  may execute timing control of the measurement system  12 , solution supply system  13 , temperature control mechanism  14 , and control mechanism  15 . 
     In the above example, the sample injection port  119  communicates with the delivery port  116   b . However, the sample injection port  119  may communicate with the introduction port  116   a . The working electrode  501  or bonding pad  221  on the base sequence detection chip  21  has a multilayered structure of Ti or Au. However, an electrode or pad made of another material may be used. The layout of the working electrodes  501  is not limited to that shown in  FIG. 16 . The numbers of working electrodes  501 , counter electrodes  502 , and reference electrodes  503  are not limited to those illustrated, either. 
     The solution supply system  13  is not limited to that shown in  FIG. 17 . For example, when a supply system which supplies a biochemical solution or a gas other than air, milli-Q water, a buffer, and an intercalating agent in accordance with the type of reaction is added, a more complex reaction can be executed in the cell  115 . Control of the biochemical solution or air supply path or supply amount between the pipes may be done by a mechanism other than a solenoid valve. The operation of the solution supply system  13  shown in  FIG. 18  is merely an example, and various changes and modifications can be made in accordance with the purpose of reaction. 
       FIGS. 30 to 32  show a case wherein the base sequence automatic analyzing apparatus  1  is used for type determination. However, this is merely an example. The base sequence automatic analyzing apparatus  1  may be used for another analyzing purpose. The automating method shown in  FIG. 33  is also merely an example. The automating sequence can also be changed in various ways by changing the arrangements of the chip cartridge  11 , measurement system  12 , solution supply system  13 , temperature control mechanism, and control mechanism  15  in various ways. 
     The relationship between the base sequence detection chip  21  and the chip cartridge top cover  112  may be reversed. 
     The layout of the channels  601   a  to  601   d  is not limited to that shown in  FIG. 5B . For example, the detection channels  601   a  may be arranged in parallel to a line that connects the cell hole portions  115   a  and  115   b . Each of the channels  601   a  to  601   d  may have a curved shape instead of a linear shape. In the above example, the introduction port  116   a  and delivery port  116   b  extend perpendicularly to the cell bottom surface. However, the present invention is not limited to this. The introduction port  116   a  and delivery port  116   b  may extend in parallel to the cell bottom surface. 
     Second Embodiment 
     This embodiment is related to a modification to the first embodiment. This embodiment is related to a modification of the arrangement of the base sequence automatic analyzing apparatus  1  shown in  FIG. 1  of the first embodiment. In this embodiment, any arrangement that is not particularly mentioned is the same as in the first embodiment, and a detailed description thereof will be omitted. 
       FIG. 35  is a view showing the overall arrangement of a base sequence automatic analyzing apparatus  700  according to this embodiment. The base sequence automatic analyzing apparatus  700  comprises a housing  701  and a computer  16 . The housing  701  corresponds to the arrangement of the chip cartridge  11 , measurement system  12 , solution supply system  13 , temperature control mechanism  14 , and control mechanism  15  in  FIG. 1 . 
     The housing  701  has two slide stages  702   a  and  702   b  at predetermined portions on the front surface. Each of the slide stages  702   a  and  702   b  has a cassette loading groove  792 . When cassettes  703  are set in the cassette loading grooves  792 , the cassettes  703  can be positioned and arranged with respect to the slide stages  702   a  and  702   b . More specifically, the slide stages  702   a  and  702   b  are designed to slide in the horizontal direction with respect to the housing  701 . This slide operation can be done using slide operation buttons  704   a  and  704   b . When one of the slide operation buttons  704   a  and  704   b  is pressed, a slide instruction signal is transmitted to a control mechanism  15 . Upon receiving the slide instruction signal, the control mechanism  15  can drive a stage driving mechanism  891  (not shown) to slide a corresponding one of the slide stages  702   a  and  702   b .  FIG. 73  is a functional block diagram of the control mechanism  15  and its constituent elements. 
     A display section  893  is arranged at another portion on the front surface of the housing  701 . Information detected by the control mechanism  15  can be displayed on the display section  893  on the basis of a command from the control mechanism  15 . Examples of detection information are a cassette type, the presence/absence of a cassette, the presence/absence of a seal, the slide stage driving state (tray open/close), the cam rotation state (e.g., the presence/absence of rotation), valve unit/probe unit driving state (e.g., the presence/absence of positioning of a nozzle/electric connector), and the inspection process progress situation. 
     When the slide operation buttons  704   a  and  704   b  are pressed while the slide stages  702   a  and  702   b  are kept accommodated in the housing  701 , the slide stages  702   a  and  702   b  slide from the housing  701  in a direction indicated by arrows in  FIG. 35 . Accordingly, the cassette loading groove  792  can unload the cassette  703  from the housing  701 . Alternatively, the cassette  703  can be set in the cassette loading groove  792 . 
     After the cassettes  703  are set in the cassette loading grooves  792 , the slide operation buttons  704   a  and  704   b  are pressed. Then, the slide stages  702   a  and  702   b  slide in a direction reverse to that of the arrows in  FIG. 35  and are accommodated in the housing  701 . 
     In the housing  701 , nozzles  707   a ,  707   b ,  708   a , and  708   b  are inserted into nozzle insertion holes  722  and  723  of the cassettes  703 . In addition, electric connectors  730  are inserted into electric connector ports  724  and  725  so that a base sequence detection operation is executed. 
     The nozzles  707   a  and  708   a  are arranged in a valve unit  705   a  on the side of the slide stage  702   a . The nozzles  707   b  and  708   b  are arranged in a valve unit  705   b  on the side of the slide stage  702   b . The electric connectors  730  are arranged in each of probe units  710   a  and  710   b  of the slide stages  702   a  and  702   b.    
       FIGS. 57A and 57B  are views showing the structure of the probe unit  710   a  including the electric connectors  730 .  FIG. 57A  is a perspective view.  FIG. 57B  is a side view. The two electric connectors  730  are arranged at a predetermined interval on the probe unit  710   a  made of, e.g., a glass epoxy substrate. At the distal end of each electric connector  730 , a plurality of projecting electrodes  730   a  are laid out in the same matrix as that of pads on a substrate  714 . When the projecting electrodes  730   a  come into contact with the pads on the substrate  714 , electrical connection between the substrate  714  and the probe unit  710   a  is ensured. The electric connector  730  has wires inside. The projecting electrodes  730   a  and control mechanism  15  are electrically connected by the wires. 
       FIG. 58  is a side view of the driving system such as the nozzles  707   a  and  708   a  and the electric connector  730 , and the cassette  703 .  FIG. 58  mainly shows the arrangement on the side of the slide stage  702   a . However, the arrangement on the side of the slide stage  702   b  is the same as that on the side of the slide stage  702   a.    
     The probe unit  710   a  is integrated with the valve unit  705   a . The valve unit  705   a  and probe unit  710   a  are simultaneously driven by a valve unit/probe unit driving mechanism  706   a . The valve unit/probe unit driving mechanism  706   a  drives the valve unit/probe unit in accordance with an instruction from the control mechanism  15 . The valve unit/probe unit driving mechanism  706   a  has two driving directions, i.e., the vertical direction and horizontal direction, as indicated by arrows in  FIG. 58 . With this structure, the nozzles  707   a  and  708   a  and electric connectors  703  move horizontally and downward with respect to the upper portion of the cassette  703  on the side of the slide stage  702   a . The nozzles  707   a  and  708   a  are positioned to the nozzle insertion holes  722  and  723 , and the electric connectors  703  are positioned to the electric connector ports  724  and  725 . Similarly, on the side of the slide stage  702   b , when a valve unit/probe unit driving mechanism  706   b  is driven, the nozzles  707   b  and  708   b  and electric connectors  703  are positioned to the nozzle insertion holes  722  and  723  and electric connector ports  724  and  725 , respectively. Accordingly, the solution supply system and the channel in the cassette  703  communicate. When the electric connectors  730  are positioned to the pads of the cassette  703 , the pads and the electric connectors  730  are electrically connected. 
     In this state, a biochemical solution or the like can be supplied from a solution supply mechanism (not shown) through the nozzles  707   a  and  707   b  and discharged through the nozzles  708   a  and  708   b . The electric connectors  730  are also electrically connected to a measurement system  12 . When a voltage is applied to the substrate  714  through the electric connectors  730 , and a current is detected, electrochemical measurement can be executed. To unload the cassettes  703  from the housing  701 , the slide operation buttons  704   a  and  704   b  are pressed. Then, the valve unit/probe unit driving mechanisms  706   a  and  706   b  drive and move the valve units  705   a  and  705   b  upward and then slide the slide stages  702   a  and  702   b  in the direction indicated by the arrows in  FIG. 35 . Accordingly, the cassettes  703  can be unloaded. 
     In this example, a valve unit  705  and probe unit  710  are integrally formed. However, the present invention is not limited to this. The valve unit  705  and probe unit  710  may be separately formed and moved vertically by separate elevating driving mechanisms. In this example, 3-electrode systems  761  to which probe DNA is immobilized and pads  762  and  763  are formed on the same surface of the substrate  714 . However, the present invention is not limited to this. The 3-electrode systems  761  may be formed on the upper surface of the substrate  714  while the pads  762  and  763  may be formed on the opposite surface. In this case, the valve unit  705  is arranged on the upper side of the cassette  703  and the probe unit  710  is arranged on the lower side. In this case, the valve unit  705  and probe unit  710  are inevitably separated. 
     Although not illustrated in  FIG. 35 , the base sequence automatic analyzing apparatus  700  incorporates the measurement system  12  which extracts an electrical signal from the base sequence detection chip in the cassette  703  or sends a signal, a temperature control mechanism  14 , and the control mechanism  15 . The control mechanism  15  in the base sequence automatic analyzing apparatus  700  is connected to the computer  16 . 
       FIG. 56  is a view showing an example of the arrangement of the base sequence automatic analyzing apparatus  700  in loading the cassette  703 . When the slide operation buttons  704   a  and  704   b  are pressed, the slide stages  702   a  and  702   b  slide from the housing  701  so that the cassette loading grooves  792  each having a predetermined depth appears outside the housing  701 . Each cassette loading groove  792  has a temperature adjustment mechanism  720 , positioning pins  709   a  and  709   b , and a cassette type determination pin  789 . 
     As the temperature adjustment mechanism  720 , for example, a Peltier element is used. The cassette  703  is loaded such that the positioning pins  709   a  and  709   b  are inserted into cassette positioning holes  728   a  and  728   b  (to be described later), and the temperature adjustment mechanism  720  is positioned to a temperature adjustment window portion  743 . In this cassette loaded state, a microswitch  811  is pressed by the cassette  703  to detect that the cassette  703  is loaded. The microswitch  811  is connected to the control mechanism  15 . The switch change-over state can always be confirmed by the control mechanism  15 . 
       FIGS. 69A and 69B  are views for explaining the detection operation of the microswitch  811 . As shown in  FIG. 69A , the microswitch  811  is arranged on the surface of the cassette loading groove  792  of the slide stage  702   a . When the cassette  703  is not loaded, the microswitch  811  projects from the surface of the cassette loading groove  792 . When the cassette is loaded, the cassette  703  presses the microswitch  811 , as shown in  FIG. 69B . This press operation is detected by the control mechanism  15  connected to the microswitch  811 . When the cassette  703  is unloaded from the cassette loading groove  792 , the microswitch  811  returns to the state shown in  FIG. 69A , i.e., projects from the groove surface. Hence, loading of the cassette can be repeatedly detected. 
     On the basis of the same principle as that of the microswitch  811 , the type of cassette is determined by detecting the presence/absence of press of the cassette type determination pin  789 . If the cassette  703  has a cassette type determination hole  749 , the cassette type determination pin  789  is not pressed when the cassette is loaded. If the cassette has no cassette type determination hole  749 , the cassette type determination pin  789  is pressed even when the cassette  703  is loaded. A signal representing the presence/absence of press of the cassette type determination pin  789  is output to the control mechanism  15 . On the basis of the signal representing the presence/absence of pin press, the control mechanism  15  can determine the type of cassette. When a sensor that detects the degree of press of the cassette type determination pin  789  stepwise is used, a plurality of types of cassettes can be determined. In this case, the depth of the cassette type determination hole  749  is adjusted in accordance with the determinable degree of press. 
     After loading the cassettes, the slide operation buttons  704   a  and  704   b  are pressed to slide the slide stages  702   a  and  702   b  into the housing  701  (the direction indicated by the arrow in  FIG. 56 ) so that the cassettes  703  are accommodated in the housing  701 . 
       FIG. 36  is a perspective view of the cassette  703 . The cassette  703  comprises a cassette top cover  711 , cassette bottom cover  712 , packing  713  (seal member), and the substrate  714 . The inner surfaces of the cassette top cover  711  and cassette bottom cover  712  are made to oppose each other and fixed while inserting the packing  713  and substrate  714  between the cassette top cover  711  and the cassette bottom cover  712 . Thus, the cassette  703  is completed. 
     The nozzle insertion holes  722  and  723  each having an almost circular section are formed to extend from an outer surface  721  to an inner surface  729  of the cassette top cover  711 . The inner diameter of the nozzle insertion holes  722  and  723  is set to be slightly larger than the outer diameter of nozzles  707  and  708  and the introduction and delivery ports  752  and  753 . The inner diameter of the nozzle insertion holes  722  and  723  is, e.g., about 3.2 mm. 
     The electric connector ports  724  and  725  each having an almost rectangular section are formed to extend from the outer surface  721  to the inner surface  729 . Each of the electric connector ports  724  and  725  are used upon receiving the electric connector  730  (to be described later). 
     A seal detection hole  726  is formed to be extend from the outer surface  721  to the inner surface  729 . The seal detection hole  726  is used to detect the presence/absence of a seal  750 .  FIG. 67A  is a view showing a state wherein the seal  750  is attached in injecting a sample into the cassette.  FIG. 67B  is a view showing a state wherein the seal  750  is peeled after a sample is injected into the cassette. In the state shown in  FIG. 67A , the seal detection hole  726  and electric connector ports  724  and  725  are covered with the seal  750 . In the state shown in  FIG. 67B , the seal  750  is not present, and the seal detection hole  726  and electric connector ports  724  and  725  are exposed. As shown in  FIG. 67A , the seal  750  is adhered from the surface of the seal detection hole  726  on the outer surface  721  of the cassette  703  to the surfaces of the electric connector ports  724  and  725 . A sample is injected into the cassette  703  while keeping the seal  750  adhered. With this structure, even when the sample solution undesirably drops to the electric connector port  724  or  725 , the solution does not enter the actual port  724  or  725 , and any problem such as an electrical short circuit is not posed because the port  724  or  725  is covered with the seal  750 . After the sample is injected, the seal  750  is peeled. 
       FIG. 68  is a view showing an example of a mechanism to detect the presence/absence of the seal on the seal detection hole  726 . As shown in  FIG. 68 , a detection light irradiation means  812  such as an LED and a detection photosensor  813  such as a photosensor are arranged such that detection light passes through a detection light passing hole  702   e  and the seal detection hole  726  at a position where the slide stage  702   a  is accommodated in the housing  701 . More specifically, the detection light irradiation means  812  and detection photosensor  813  are arranged to oppose each other via the cassette  703  so that the detection light passing hole  702   e  and seal detection hole  726  are located on the optical path of the detection light when the slide stage  702   a  is accommodated. 
     The detection light irradiation means  812  and detection photosensor  813  may be fixed on the housing  701 . Alternatively, only the detection light irradiation means  812  may be fixed on the housing  701  while the detection photosensor  813  may be fixed on the slide stage  702   a . The detection light irradiation means  812  emits the detection light and the detection photosensor  813  detects it on the basis of an instruction from the control mechanism  15 , and the detection photosensor  813  outputs a detection signal to the control mechanism  15 . 
     The detection light is emitted such that it passes through the detection light passing hole  702   e  and seal detection hole  726 , which are formed to extend from the groove surface to the bottom surface of the slide stage  702   a . The photosensor  813  detects the light that has passed through the detection light passing hole  702   e  and seal detection hole  726 . The detection signal is transmitted to the control mechanism  15 . 
     In the state shown in  FIG. 67A  wherein the seal  750  is adhered to the cassette  703 , the detection light is shielded by the seal  750 . Hence, the detection photosensor  813  cannot detect the detection light. In the state shown in  FIG. 67B  wherein the seal  750  is peeled, the detection light is detected by the detection photosensor  813  without being shielded. 
     Accordingly, it can be detected whether the seal  750  of the cassette  703  is peeled. More specifically, even when the cassette  703  is set on the stage without peeling the seal  750 , the nozzles  707   a ,  707   b ,  708   a , and  707   b  and the electric connectors  730  are prevented from moving downward and coming into contact with the seal  750 . 
       FIG. 37  is a perspective view of the cassette top cover  711  viewed from the side of the inner surface  729 . 
     On the side of the inner surface  729 , a substrate positioning groove  731  having a predetermined depth and almost the same sectional shape as that of the substrate  714  is formed. The substrate positioning groove  731  is surrounded by the inner surface  729 . The substrate positioning groove  731  is formed to overlap the nozzle insertion holes  722  and  723  and the electric connector ports  724  and  725 . When the substrate  714  is fitted in the substrate positioning groove  731 , the substrate  714  can be positioned and arranged in the cassette top cover  711 . The depth of the substrate positioning groove  731  is almost the same as the thickness of the substrate  714 . 
     A packing positioning groove  732  deeper than the substrate positioning groove  731  is formed to overlap the substrate positioning groove  731  on the side of the inner surface  729 . The packing positioning groove  732  is surrounded by the substrate positioning groove  731 . The packing positioning groove  732  is formed to overlap the nozzle insertion holes  722  and  723 . When the packing  713  is fitted in the packing positioning groove  732 , the packing  713  can be positioned and arranged in the cassette top cover  711 . The depth of the packing positioning groove  732  with respect to the substrate positioning groove  731  is almost the same as the thickness of a packing main body  751  (to be described later). Hence, the depth of the packing positioning groove  732  with respect to the inner surface  729  is almost the same as a thickness obtained by adding the thickness of the substrate  714  to the thickness of the packing main body  751 . 
     Four threaded holes  727   a ,  727   b ,  727   c , and  727   d  are formed at the periphery portion of the inner surface  729 . With the threaded holes  727   a  to  727   d , the cassette top cover  711  and cassette bottom cover  712  can be fixed by screwing. 
     Two cassette positioning holes  728   a  and  728   b  are formed at the peripheral portion of the inner surface  729 . When the cassette  703  is set while aligning the cassette positioning holes  728   a  and  728   b  to two positioning pins provided on each of the slide stages  702   a  and  702   b , the cassette  703  can be positioned to each of the slide stages  702   a  and  702   b.    
       FIG. 38  is a plan view of the cassette bottom cover  712  viewed from an outer surface  741 . The temperature adjustment window portion  743  is formed to extend from the outer surface  741  to an inner surface  742 . The substrate  714  is arranged on the side of the inner surface  742  of the temperature adjustment window portion  743 . When the substrate  714  is arranged to come into contact with the temperature adjustment mechanism  720  arranged on each of the slide stages  702   a  and  702   b  through the temperature adjustment window portion  743 , the temperature of the substrate  714  can be adjusted from the side of the cassette bottom cover  712 . 
     The outer surface  741  has a bar code  744 . The identification number of the cassette  703  is written as bar code information of the bar code  744 . When the bar code  744  with the identification number is read by a bar code reading means, the cassette  703  can be identified. 
     A seal detection hole  746  is formed to extend through the outer surface  741 . The seal detection hole  746  of the cassette bottom cover  712  is formed at a position where the seal detection hole  746  communicates with the seal detection hole  726  of the cassette top cover  711  when the cassette top cover  711  and cassette bottom cover  712  are fixed. Accordingly, when the cassette top cover  711  and cassette bottom cover  712  are fixed, the seal detection hole  726  which extends from the cassette top cover  711  to the cassette bottom cover  712  is formed. When the seal detection hole  726  is irradiated with the detection light, the presence/absence of the seal  750  can be detected. 
     Four threaded holes  747   a ,  747   b ,  747   c , and  747   d  are formed at the peripheral portion of the outer surface  741 . Each of the threaded holes  747   a  to  747   d  and a corresponding one of the threaded holes  727   a  to  727   d  formed in the cassette top cover  711  are screwed. Accordingly, the cassette bottom cover  712  can be fixed to the cassette top cover  711 . 
     Two cassette positioning holes  748   a  and  748   b  are formed at the peripheral portion of the outer surface  741 . The cassette  703  is set while aligning the cassette positioning holes  748   a  and  748   b  to two positioning pins provided on each of the slide stages  702   a  and  702   b . Accordingly, the cassette  703  can be positioned to each of the slide stages  702   a  and  702   b.    
     Reference numeral  749  denotes the cassette type determination hole  749 . The type of cassette can be determined on the basis of the presence/absence of the hole. The type determination can be automatically done on the basis of the presence/absence of press of the cassette type determination pin  789 . The pin press state of the cassette type determination pin  789  is detected by the control mechanism  15 . In the following example, the cassette  703  having the cassette type determination hole  749  is used. Even when the cassette  703  having no cassette type determination hole  749  is used, the same measurement can be executed except that the type of cassette to be determined is different. Alternatively, the control mechanism  15  may cause the display section  893  to display a warning representing that the type of cassette  703  is different and prevent the measurement process from starting. Alternatively, a fixed pin may be used as the cassette type determination pin  789  such that the cassette  703  having no cassette type determination hole  749  cannot be loaded. Accordingly, any erroneous cassette  703  may be prevented from being set. 
       FIG. 39  is a perspective view of the packing  713 . The packing  713  comprises the packing main body  751 , introduction port  752 , and delivery port  753 . The packing main body  751  has an almost rectangular shape and a predetermined thickness. The four corners of the packing main body  751  are cut. The introduction port  752  and delivery port  753  are ports each having a cylindrical shapes. The introduction port  752  and delivery port  753  are arranged on the major surface of the packing main body  751  near the two ends along the long sides and near the central portion along the short sides. The introduction port  752  and delivery port  753  have, at their distal ends, opening portions  754  and  755 , respectively. Channels  756  and  757  are formed through the axes of the introduction port  752  and delivery port  753  to extend from the opening portions  754  and  755  to the packing main body  751  in a direction perpendicular to the major surface of the packing main body  751 . A groove  758  having a curved shape is formed on the lower surface of the packing main body  751  from the formation position of the introduction port  752  to the formation position of the delivery port  753 . The lower surface of the packing main body  751  is almost flat. The groove  758  is connected to the channels  756  and  757 . The sectional areas of the channels  756  and  757  and the groove  758  are almost the same. 
       FIG. 40  is a plan view of the packing  713 . The groove  758  goes from the channel  756  toward the channel  757 , curves at a predetermined curvature, turns, and goes again from the channel  757  to the channel  756 . the groove  758  is formed in this way such that it repeatedly turns a plurality of number of times between the channels  756  and  757 . When each turn of the groove  758  has a curve at a predetermined curvature, any residual biochemical solution or air generated when a corner of a turn is formed can be suppressed. 
       FIG. 41  is a plan view of the substrate  714 . The 3-electrode systems  761  and the pads  762  and  763  are formed on the major surface of the substrate  714 . The 3-electrode system  761  and pad  762 , and the 3-electrode system  761  and pad  763  are connected by wiring lines (not shown). The 3-electrode systems  761  are electrodes each formed from a combination of a working electrode, counter electrode, and reference electrode shown in the first embodiment. DNA probes are immobilized to the working electrodes. 
       FIG. 41  shows the layout of the substrate  714  and the packing  713  which overlaps a portion of the substrate  714 . Reference numeral  764  denotes a packing arrangement position  764 ; and  765 , a channel formation position. The 3-electrode systems  761  are formed at the packing arrangement position  764  while aligning to the channel formation position  765 . Accordingly, when the packing  713  and substrate  714  are positioned to the cassette top cover  711  and cassette bottom cover  712  and fixed between them, a channel is formed by the groove  758  and the surface of the substrate  714 . In addition, the 3-electrode systems  761  are exposed to the surface of the channel. More specifically, a gap is formed on the 3-electrode systems  761  by the groove  758 . A channel is formed by the gap. In this state, sealing between the packing  713  and the substrate  714  is held. 
     Reference numerals  766  and  767  denote regions where the electric connector ports  724  and  725  are arranged when the packing  713  and substrate  714  are sandwiched and fixed between the cassette top cover  711  and the cassette bottom cover  712 . The electric connectors  730  come into contact with pads  762  and  763  formed in the electric connector formation positions  766  and  767  through the electric connector ports  724  and  725 . Accordingly, the 3-electrode systems  761  and the electric connector  730  arranged through the electric connector port  724  or the 3-electrode system  761  and the electric connector  730  arranged through the electric connector port  725  can be rendered conductive. 
     The packing arrangement position  764  functions as a sensor region where a DNA probe is immobilized, and the presence/absence of hybridization is detected by an electrochemical reaction. The pads  762  and  763  function as electrical contact regions where an electrical signal is extracted from the substrate  714  to the outside of the cassette  703 . The sensor regions and electrical contact region are separately arranged. 
       FIGS. 42 and 43  are views showing the assembled state of the cassette  703  viewed from the side of the cassette top cover  711  and the side of the cassette bottom cover  712 , respectively. 
     First, the packing  713  is fitted into the packing positioning groove  732  while aligning them to each other such that the introduction port  752  and delivery port  753  are inserted into the nozzle insertion holes  722  and  723 . Next, the substrate  714  is positioned to the substrate positioning groove  731  such that the major surface of the substrate  714 , i.e., the surface on which the 3-electrode systems  761  and pads  762  and  763  are formed faces the side of the cassette top cover  711 . Next, the cassette bottom cover  712  is placed on the cassette top cover  711  such that the inner surface  742  faces the side of the cassette top cover  711 , and the positions of the threaded holes  747   a  to  747   d  correspond to those of the threaded holes  727   a  to  727   d . Screws  770   a  to  770   d  are threadably inserted into the threaded holes  747   a  to  747   d  and threaded holes  727   a  to  727   d . Accordingly, the cassette top cover  711  and cassette bottom cover  712  are threadably attached to each other. In addition, the packing  713  and substrate  714  are sandwiched and fixed between the cassette top cover  711  and the cassette bottom cover  712 . Thus, the cassette  703  is completed. In this complete state, a channel is formed from the nozzle insertion hole  722  to the nozzle insertion hole  723  while communicating sequentially through the opening portion  754 , channel  756 , groove  758 , channel  757 , and opening and  755 . 
       FIGS. 42 and 43  show an example in which the cassette top cover  711  and cassette bottom cover  712  are fixed by screwing. However, the present invention is not limited to this. For example, an engaging method using projecting and recess members may be used.  FIG. 59  is a view showing an example of the structure of a cassette  821  fixed by engaging. As shown in  FIG. 59 , a total of six engaging holes  824  are formed in a cassette top cover  822 . That is, three engaging holes are formed in each of the side portions of the cassette top cover  822  to extend from the inner wall to the outer wall. On the other hand, a total of six pawl-shaped engaging members  825  are formed in a cassette bottom cover  823 . That is, three engaging members  825  are formed on the inner surface of each of the two side portions of the cassette bottom cover  823 . The components except the engaging members  825  and engaging holes  824  are the same as those of the cassette top cover  711  and cassette bottom cover  712  shown in  FIGS. 42 and 43 , and a detailed description thereof will be omitted. 
     When each of the engaging members  825  and a corresponding one of the engaging holes  824  engage at, e.g., a position indicated by the alternate long and short dashed line in  FIG. 60A , the cassette top cover  822  and cassette bottom cover  823  are fixed by engaging, as shown in  FIG. 60B . 
       FIG. 44  is a sectional view of the side surface of the cassette  703  which is completed in accordance with the procedures shown in  FIGS. 42 and 43 . As shown in  FIG. 44 , the cassette  703  has a total of three types of openings. 
     The first openings are openings formed by the packing positioning groove  732  and nozzle insertion holes  722  and  723 . With the first openings, the nozzles  707  are attached to positions corresponding to the projecting portions (ports) of the packing  713 . Hence, a biochemical solution or air can be introduced or delivered. In addition, a sample solution can be injected using a pipette or the like. 
     The second openings are openings which are formed in the same surface as that of the first openings while being separated from the portion where the packing  713  is fixed, and formed by the electric connector ports  724  and  725 . In the second openings, the pads  762  and  763  to obtain an electrical contact between the substrate  714  and the apparatus main body are arrayed. The probe units (electric connectors  730 ) arranged in the apparatus main body are inserted into the second openings. Accordingly, the electrical contact with the pads on the substrate  714  can be obtained. 
     The third opening is formed in the surface that is opposite to that of the first and second openings via the substrate  714 . The third opening is formed at a position corresponding to the lower surface of the portion where the packing  713  is fixed, i.e., in the lower surface of the first openings. With the third opening, the temperature control mechanism  14  can come into direct contact with the lower surface of the substrate  714  so that the temperature of the substrate  714  can be controlled. 
     More specifically, the nozzle  707  is pressed again the nozzle insertion hole  722  in the direction indicated by an arrow. The electric connector  730  is inserted into each of the electric connector ports  724  and  725 . The lower surface side of the substrate  714 , i.e., the side where the 3-electrode systems  761  are not formed is exposed through the temperature adjustment window portion  743 . The cassette  703  is placed on the slide stage  702  such that the temperature adjustment mechanism  720  comes into contact with the exposed surface. Accordingly, the temperature of the substrate  714  can be adjusted from the lower surface side. 
       FIG. 45  is a sectional view of the channel of the cassette  703 . The nozzle  707  and nozzle  708  are inserted into the nozzle insertion holes  722  and  723  and pressed against the introduction port  752  and delivery port  753  of the packing  713 . With this structure, the nozzle  707  and nozzle  708  communicate with the introduction port  752  and delivery port  753 . In this state, a biochemical solution or air is supplied from the nozzle  707 . The biochemical solution or air is delivered from the nozzle  708  through the channel formed by the groove  758  formed in the packing  713  and the substrate  714 . 
       FIGS. 46 to 51  are views showing the detailed structures of the port tip shape of the packing  713 . 
       FIG. 46  shows the first example of the port tip shape. An inner diameter r 1  of the opening portions  754  and  755  at the distal end portions of the introduction port  752  and delivery port  753  is formed to be larger than an inner diameter r 2  of the channels  756  and  757  stepwise, i.e., discontinuously. The material of the packing  713  is silicone rubber. The hardness is, e.g., about 60. The packing  713  is formed by injection molding using a mold to be integrated with the packing main body  751 , introduction port  752 , delivery port  753 , and the channels. A depth g 1  (corresponding to the height of the channel) of 658 is about 0.7 mm. A width w 1  is about 1 mm. A height h 1  of each of the introduction port  752  and delivery port  753  is about 4 mm. An outer diameter R 1  is about 3 mm. The inner diameters r 1  and r 2  are respectively, e.g., r 1 =about 2 mm and r 2 =about 1 mm. A height h 2  of the portion with the inner diameter r 1  is, e.g., about 0.5 mm. A thickness h 3  of the packing main body  751  is about 3 mm. The surfaces at which the packing  713  and substrate  714  are bonded are preferably mirror-polished. 
     From the second example, the material, hardness, forming method, and dimension are the same as in the first example unless otherwise specified. 
       FIG. 47  shows the second example of the port tip shape. The inner diameter r 2  of the opening portion  754  at the distal end portion of each of the introduction port  752  and delivery port  753  is constantly about 1 mm. The outer diameter continuously decreases from the outer diameter R 1  toward the distal end. At the tip, the outer diameter is an outer diameter R 2  almost equal to the inner diameter r 2 . The angle of an outer surface  771  at the portion with the small outer diameter with respect to the major surface of the packing main body  751  is about 45°. The outer diameter becomes small in the range of about 1 mm from the distal end of each of the introduction port  752  and delivery port  753 . The outer diameter is almost constant on an outer surface  772  closer to the packing main body  751  than the outer surface  771 . The outer surface  772  may also be tilted by about 1° with respect to, e.g., an inner surface  773  such that the outer surface  772  is also slightly tapered toward the tip. This also applies to the examples shown in  FIG. 46  and  FIGS. 48 to 51 . 
       FIG. 48  shows the third example of the port tip shape. The inner diameter of the distal end portion of each of the introduction port  752  and delivery port  753  gradually increases while the outer diameter gradually decreases. More specifically, each of the introduction port  752  and delivery port  753  has a semi-circular sectional shape having, e.g., a radius a 1 =about 0.5 mm. 
       FIG. 49  shows the fourth example of the port tip shape. The outer diameter of each of the introduction port  752  and delivery port  753  is constant. The inner diameter is defined to be gradually increase toward the distal end and have a bowl shape. More specifically, from the distal end of each of the introduction port  752  and delivery port  753  to a depth of about 0.75 mm, the inner diameter gradually continuously decreases from an inner diameter r 3  (e.g., about 1.4 mm) to the inner diameter r 2 . At a deeper position, each of the introduction port  752  and delivery port  753  has the predetermined inner diameter r 2 . An inner surface  774  at the position where the inner diameter is large is tilted by about 15° with respect to the inner surface  773 . When the inner wall is formed into the bowl shape, the tip of a pipette that injects a sample can be smoothly inserted into the introduction port  752  and delivery port  753 . In addition, the sealing properties between the packing  713  and the pipette can be increased. Hence, a sample can easily be introduced onto the substrate  714 . 
       FIG. 50  shows the fifth example of the port tip shape. Both the outer diameter and the inner diameter of each of the introduction port  752  and delivery port  753  are almost constant toward the distal end. An outer surface  775  at the distal end is almost perpendicular to the channels  756  and  757 . 
       FIG. 51  shows the sixth example of the port tip shape. Each of the introduction port  752  and delivery port  753  has almost the same basic structure as that of the example shown in  FIG. 50  except an O-ring  776  is formed at the distal end. 
     The dimensions of the port tip shapes shown in  FIGS. 46 to 51  are merely examples. They can be appropriately changed in accordance with the convenience in molding, the size of the substrate  714 , and the like. The material of the packing  713  is not limited to silicone rubber. Elastomer, Teflon, Daiflon, and any other resin can also be used. 
     The port tip need not be formed to be perpendicular to the major surface of the packing main body  751 . For example, the port tip may be tilted with respect to the major surface by a predetermined angle. Alternatively, the port tip may be formed to be perpendicular to the major surface of the packing main body  751 , bent halfway at the formation position, and then extend in a direction that is not perpendicular to the major surface of the packing main body  751 . 
       FIG. 52  is a view showing the overall arrangement of the valve unit  705 . The arrangement of the probe unit  710  is not illustrated in  FIG. 52 . In the valve unit  705 , valve bodies  781  and  782  are connected and fixed. The valve body  781  has a two-way solenoid valve  403  and three-way solenoid valves  413 ,  423 , and  433 . The valve body  782  has three-way solenoid valves  441  and  445 . The valve bodies  781  and  782  are made of, e.g., PEEK resin. If the valve bodies  781  and  782  are to be separately formed and connected, PTFE is used as a packing at the joint portion. Hence, portions of the valve bodies  781  and  782 , which come into contact with a biochemical solution, are made of PEEK and PTFE. Each of the valve bodies  781  and  782  has a cavity having an almost constant sectional shape. The cavity functions as a pipe that connects each solenoid valve (to be described later) and the packing  713 . The cavity formed in the valve body  782  communicates with the nozzles  707  and  708 . The nozzles  707  and  708  are made of PEEK resin. 
       FIG. 61  is a view showing an example of the structure of a valve unit  831  as a modification of the valve unit  705 . The valve unit  705  shown in  FIG. 52  uses the face-mounted solenoid valves  403 ,  413 ,  423 ,  433 ,  441 , and  445 . Instead, the valve unit shown in  FIG. 61  uses embedded solenoid valves  832 ,  833 ,  834 ,  835 ,  836 , and  837 . The functions of the solenoid valves  832 ,  833 ,  834 ,  835 ,  836 , and  837  are the same as those of the solenoid valves  403 ,  413 ,  423 ,  433 ,  441 , and  445 . The remaining components are the same as those of the valve unit  705 . 
       FIG. 62  is a view showing the structure of a valve unit  841  according to another modification. As shown in  FIG. 52 , the valve body  781  which has the solenoid valves  403 ,  413 ,  423 , and  433  and the valve body  782  which has the solenoid valves  441  and  445  are separate bodies. Instead, an integral valve body  842  may have the solenoid valves  403 ,  413 ,  423 ,  433 ,  441 , and  445 . 
       FIG. 63  is a view showing the structure of a valve unit  846  according to still another modification. The valve unit  846  has the two valve bodies  781  and  782 , as in  FIG. 52 . The valve bodies  781  and  782  are connected by a tube  847 . The tube  847  communicates the three-way solenoid valve  433  with the three-way solenoid valve  441 , like the pipe  435  in  FIG. 17 . When the valve unit is formed by a plurality of valve bodies, the valve bodies may be connected by a tube or the like. In this case, each valve body may have a driving mechanism. 
       FIG. 64  is a view showing the structure of a valve unit  851  according to still another modification. In the valve unit  851  according to this modification, a plurality of valve bodies  852  to  857  have the solenoid valves  403 ,  413 ,  423 ,  433 ,  441 , and  445 , respectively. The valve bodies  852  to  857  are connected and fixed by, e.g., PTFE seals. Accordingly, the valve bodies  852  to  857  function like the valve unit  705  shown in  FIG. 52 . The valve bodies  852  to  857  may be connected by tubes, as in  FIG. 63 . 
       FIG. 53  is a view showing the functional arrangement of the valve unit  705  shown in  FIG. 52 . The two-way solenoid valve  403  is not illustrated in  FIG. 52 . The same reference numerals as in the arrangement of the solution supply system  13  shown in  FIG. 17  denote the same components in  FIG. 53 , and a detailed arrangement will be omitted. 
     The valve bodies  781  and  782  have internal pipes. With these pipes, the channel of a biochemical solution or air between the three-way solenoid valves  413 ,  423 , and  433  is defined. 
     The three-way solenoid valve  413  selectively supplies air or milli-Q water to the three-way solenoid valve  423  on the downstream side. The three-way solenoid valve  423  selectively supplies a buffer or the air or milli-Q water from the three-way solenoid valve  413  to the three-way solenoid valve  433  on the downstream side. The three-way solenoid valve  433  selectively supplies a intercalating agent or the air, milli-Q water, or buffer from the three-way solenoid valve  423  to the valve body  782  on the downstream side. The three-way solenoid valve  441  switches between supply of the air or biochemical solution from the valve body  781  to the nozzle  707  and supply to the three-way solenoid valve  445  through a bypass pipe  446 . The three-way solenoid valve  445  switches supply of the air or biochemical solution from the three-way solenoid valve  441  and delivery of the biochemical solution or air from the cassette  703  through the nozzle  708 . 
     A solution supply pump  454  is arranged downstream of the cassette  703 . If a pump is provided for each of milli-Q water, a buffer, and an intercalating agent, three pumps are necessary, resulting in a bulky apparatus. Assume that a pump is arranged upstream of the cassette  703  to supply a liquid by a positive pressure. If a pipe has leakage, the solution may leak from that portion. However, as in the above arrangement, when the solution supply pump  454  is arranged downstream of the cassette  703  to supply a liquid by a negative pressure. In this case, only one common solution supply pump  454  suffices for all biochemical solutions. If a pipe has leakage, the biochemical solution is not naturally supplied. In addition, the liquid does not leak from the leakage portion of the pipe. 
     In the valve unit  705 , to supply a buffer into the cassette  703 , the three-way solenoid valves  423 ,  441 , and  445  and the solution supply pump  454  are turned on. Accordingly, the buffer is sucked up. The biochemical solution is switched to the side of the nozzle  707 . The biochemical solution is sucked up from the nozzle  707  to the cassette  703  and then from the cassette  703  to the nozzle  708 . The biochemical solution can be wasted through the three-way solenoid valve  454 . 
     To supply milli-Q water into the cassette  703 , the three-way solenoid valve  413  is turned on in place of the three-way solenoid valve  423 . To supply an intercalating agent into the cassette  703 , the three-way solenoid valve  433  is turned on in place of the three-way solenoid valve  423 . To supply air into the cassette  703 , the three-way solenoid valve  403  is turned on, and all the three-way solenoid valves  413 ,  423 , and  433  are turned off. 
     The internal capacity of the pipes of the cavity portions formed in the valve bodies  781  and  782  of the valve unit  705  is about 200 μL. As an example different from this embodiment, the three-way solenoid valves are connected by tubes to form the same flow as in this embodiment. In this case, an internal capacity of about 500 μL is necessary. As compared to this example, the amount of a reagent can greatly be decreased. In the example different from this embodiment, the internal capacity between the valve unit  705  and the cassette  703  is also as large as 100 μL or more. In this embodiment, however, the internal capacity can greatly be decreased to 10 μL. With this structure, the amount of a solution or air that undesirably flows in the cassette  703  after switching the reagent can largely be reduced. As a result, any variation in reaction or measurement can be reduced. The reproducibility of the result also largely increases. 
       FIG. 65  is a view showing a modification of the functional arrangement of the valve unit  841 . The same reference numerals as in  FIG. 53  denote the same components, and a detailed description thereof will be omitted. In the functional arrangement of the valve unit  841  shown in  FIG. 65 , to improve the reaction efficiency and reaction uniformity in the cassette  703 , a mechanism that oscillates a biochemical solution in the cassette  703  is introduced. 
     The two-way solenoid valve  403  serving as an air stop valve is arranged upstream of the valve unit  841 . In addition, a liquid oscillation mechanism  861  which oscillates a biochemical solution is arranged on the tube  863  between the two-way solenoid valve  403  and the three-way solenoid valve  411 . A leakage valve  862  is arranged downstream of the valve unit  841  between the three-way solenoid valve  445  and the solution supply pump  454 . As the liquid oscillation mechanism  861 , for example, a pinch valve is used. The two-way solenoid valve  403 , liquid oscillation mechanism  861 , and leakage valve  862  are driven on the basis of an instruction from the control mechanism  15 , like the remaining solenoid valves. 
     An example of reaction principle using the valve unit  841  will be described below. 
     The valve unit  841  is set to form a channel by air inside. More specifically, the solenoid valves  413 ,  423 , and  433  are turned off. That is, the biochemical solution supply side is blocked, and the air supply side channel is opened. In addition, the solenoid valves  441  and  445  are turned on. That is, the channel is switched from the bypass side to the side of the cassette  703 . Furthermore, the solenoid valve  403  is turned off to close the air supply channel. The leakage valve  862  is turned on to open one end of the channel. Accordingly, the channel on the air side is closed while the leakage side is opened. 
     In this state, the liquid oscillation mechanism  861  is turned on/off. The tube in the liquid oscillation mechanism  861  is repeatedly pressed and opened. Accordingly, the volume changes, and the biochemical solution onto the substrate in the cassette is oscillated. The liquid oscillation amount can be adjusted by changing the inner diameter of the tube used in the pinch valve, the tube press width, and the press area. When a tube having an inner diameter of 1 mm is pressed by a width of 5 mm, a biochemical solution of about 4 μL can be oscillated. The volume of the channel on the substrate  714 , which is formed by the packing  713  and substrate  714 , is about 30 μL. A biochemical solution corresponding to about 10% of the channel volume can be oscillated. 
     Such biochemical solution oscillation can be effectively executed in (1) hybridization process, (2) cleaning process, and (3) intercalating agent supply process. When sample DNA is oscillated in the hybridization process (1), the hybridization efficiency can be increased, and the hybridization time can be shortened. When a buffer solution is oscillated in the cleaning process (2), the efficiency of peeling nonspecific absorption DNA can be increased so that the cleaning time can be shortened. When an intercalating agent is oscillated in the intercalating agent supply process (3), the uniformity of the concentration of the intercalating agent can be increased. In addition, the intercalating agent adsorption uniformity can also be increased. As a result, any variation in signal can be reduced, and the S/N ratio can be improved. The effect of biochemical solution oscillation can be obtained either by applying the biochemical solution oscillation process to all the processes (1) to (3) or by applying the biochemical solution oscillation process to some of the processes (1) to (3). More specifically, biochemical solution oscillation can be effectively executed in, e.g., (s 21 ), (s 28 ), and (s 33 ) in the flow chart shown in  FIG. 18 . 
     In the example shown in  FIG. 65 , a pinch valve is used. However, the present invention is not limited to this.  FIGS. 66A and 66B  are views showing modifications of the liquid oscillation mechanism. 
       FIG. 66A  shows an example in which an eccentric cam  866  is used as the liquid oscillation mechanism. The eccentric cam  866  has an almost elliptical sectional shape. The eccentric cam  866  can be rotated by a cam rotating mechanism  892  about an eccentricity  867  separated from the center of the cam by a predetermined distance. The cam rotating mechanism  892  is controlled by the control mechanism  15 . The tube  863  is sandwiched and held between a fixed member  868  and a movable member  869 . When the eccentricity  867  is located between the cam center and the movable member  869 , as shown in  FIG. 66A , by rotation by the cam rotating mechanism  892 , the eccentric cam  866  is located relatively far from the movable member  869 . Hence, the tube  863  is opened without being pressed. On the other hand, when the cam center is located on the opposite side of the movable member  869 , unlike  FIG. 66A , the movable member  869  is pressed against the fixed member  868  by the eccentric cam  866 . The tube  863  is pressed between the fixed member  868  and the movable member  869 . When the eccentric cam  863  repeatedly rotates, the press state and open state of the tube  863  are repeated. As a result, the biochemical solution in the tube  863  oscillates. 
       FIG. 66B  shows a further modification of the structure shown in  FIG. 66A . Instead of the eccentric cam  866  in  FIG. 66A , a cam  870  with projections is used. The cam  870  with projections has an almost cylindrical shape and a plurality of projections  871  formed on the outer side surface. When the cam  870  with projections is used, the tube  863  is pressed or not pressed in accordance with the position of the projection  871  during rotation. When one projection  871  is located on the side of the movable member  869 , the movable member  869  is pressed to the side of the fixed member  868  so the tube  863  is pressed. When a projection  871  is shifted from the position on the side of the movable member  869 , the tube  863  is not pressed. 
     Alternatively, the internal rotating mechanism in a Perista pump may be applied. As a more sophisticated method, the volume in the pipe may be changed by using a piezoelectric element, or a syringe pump may be used. In this way, any other arrangement that can oscillate a biochemical solution can be applied. 
       FIGS. 54A to 54D  are views showing the detailed structures of the tip shape of the nozzle  707 . 
       FIGS. 54A to 54D  show various modifications of the tip shape. It is effective to appropriately change the nozzle tip shape in accordance with the shape of the distal end of the packing  713 . 
     For example, as shown in  FIG. 51 , when the packing  713  having the O-ring  776  formed at the distal end portion is used, the structure shown in  FIG. 54A  is preferably used. As shown in  FIG. 54A , an outer surface  801  is formed to be flat and perpendicular to a channel  802 . With this structure, the sealing properties between the nozzles and the packing  713  can be kept satisfactory, so an alignment margin against misalignment can be generated. An outer diameter R a  of the nozzle  707  is about 3 mm. An inner diameter r a  of the nozzle  707  is about 1 mm. 
     For example, when the nozzle  707  is to be inserted into the packing  713 , as shown in  FIG. 46  or  49 , the structure shown in  FIG. 54B  can effectively be used. As shown in  FIG. 54B , the inner diameter is constant, although the outer diameter gradually decreases from a predetermined height to the distal end portion. Hence, an outer surface  803  is tilted with respect to the channel  802  by, e.g., 15°. Accordingly, the nozzle can properly be inserted and sealed to the large-diameter opening at the distal end of each of the introduction port  752  and delivery port  753  shown in  FIG. 46  or  49 . In these combinations, however, the axes of the packing and the nozzle must be strictly aligned. Even when the packing shown in  FIG. 49  is combined with the nozzle shown in  FIG. 54A , the airtightness can sufficiently be maintained. In addition, an alignment margin can be obtained. 
     For example, when the distal end of the packing  713  is flat, as shown in  FIG. 50 , or has a recess, the structure shown in  FIG. 54C  is effective. As shown in  FIG. 54C , the distal end portion has an O-ring  804 . 
     For example, when the packing  713  has a distal end with an acute angle, as shown in  FIG. 47 , and the sealing properties are to be held inside the nozzle  707  the structure shown in  FIG. 54D  is effective. As shown in  FIG. 54D , the inner diameter of the channel  802  is constant up to a predetermined height and then continuously increases toward the distal end. 
     The present invention is not limited to the above combinations. The tip shape of the nozzle  707  can be appropriately changed from the viewpoint of sealing properties and alignment margin in accordance with the shape of the introduction port  752  and delivery port  753  of the packing  713 . 
       FIGS. 54A to 54D  show the examples of the shape of the nozzle  707 . This also applies to the nozzle  708 . 
       FIG. 55A  is a view showing a sample injection operation to the delivery port  753  by using a pipette  791 . Referring to  FIG. 55A , the packing  713  is indicated by the delivery port  753  shown in  FIG. 49 . As shown in  FIG. 55A , the distal end of the pipette  791  reaches the channel  757  along the inner surface  774  of the delivery port  753 . The outer surface of the pipette  791  is almost in tight contact with the inner surface of the delivery port  753 . If a sample is injected before the nozzle inner surface and pipette outer surface completely come into tight contact with each other, the sample may not be supplied onto the substrate  714 . In addition, if the degree of contact is low, the sample does not flow downward and instead leaks upward from the delivery port  753 . When the structure shown in  FIG. 55A  is obtained, the sample can be injected in an almost sealed state. Hence, any liquid leakage can be reduced. 
       FIG. 55B  shows a state wherein the nozzle  708  is pressed against the delivery port  753  and sealed. In the examples shown in  FIGS. 55A and 55B , the tip shape of the delivery port  753  shown in  FIG. 49  and the tip shape of the nozzle  708  shown in  FIG. 54A  are combined. As shown in  FIG. 55B , the distal end of the nozzle  708  is pressed against the distal end of the delivery port  753 . The delivery port  753  and nozzle  708  are sealed. In this state, a biochemical solution or air is transferred to the side of the nozzle  708  in the direction indicated by the arrow. 
     The combination of the nozzle  708  and delivery port  753  shown in  FIG. 55B  is supposed to be optimum, in which the upper surface of the packing and the lower surface of the nozzle are in contact and sealed. The reason why the combination shown in  FIG. 55B  is optimum will be described in comparison with combinations with sealing in  FIGS. 74A to 74C . 
       FIG. 74A  is a sectional view of the seal state of a nozzle  901  and a delivery port  902 . The inner diameter of the opening portion at the distal end portion of the nozzle  901  is formed to be stepwise larger than that of the proximal portion closer to the valve unit  705  than the distal end portion. The distal end of the delivery port  902  is inserted and sealed to an insertion hole  901   a  of the distal end portion having the large inner diameter. The outer diameter of the nozzle  705  is constant. 
     The inner diameter of the distal end of the delivery port  902  is constant while the outer diameter gradually decreases toward the distal end. That is the distal end of the delivery port  902  has a taper  902   a . In the combination of the nozzle  901  and delivery port  902 , even the gap between the insertion hole  901   a  and the outer side surface of the delivery port  902  is filled with a biochemical solution. Hence, for example, as shown in  FIG. 74B , when the nozzle  901  is moved upward and separated from the delivery port  902 , the biochemical solution may flow from the taper  902   a  on the outer side surface of the delivery port  902  and contaminate the periphery. In base sequence inspection of DNA or the like, even slight contamination may cause a determination error. Hence, such biochemical solution overflow poses a problem. 
     Especially, the gap between the outer wall of the delivery port  902  and the inner wall of the nozzle  901  is “hidden” from the flow of the biochemical solution. When a DNA solution in the delivery port  902  is sucked for the first time, the “hidden” portion is filled with the solution first, and then, the solution is sucked. Then, a reagent such as a cleaning solution is supplied. However, the portion where the DNA solution has entered first is “hidden” from the flow. For this reason, the solution at that portion cannot be sufficiently diluted. That is, the biochemical solution hardly circulates at the “hidden” portion. 
     Even after the end of inspection, the DNA solution having a relatively high concentration remains at a high probability. For this reason, the problem of contamination becomes serious. In addition, a buffered solution is often used as a reagent. When water evaporates after inspection, a crystal may be formed. In this structure, the delivery port  902  and nozzle  901  are sealed “linearly”. If a crystal is generated on the sealing line, sufficient sealing is impossible. It may lead to a solution supply error such as leakage. In case of leakage, the periphery is contaminated by the liquid. In addition, the electrical system may be short-circuit. 
       FIG. 74C  shows another seal combination. A nozzle  911  has a constant inner diameter, like the delivery port  902  shown in  FIG. 74A , and a taper  911   a  where the outer wall of the distal end portion is gradually tapered toward the distal end. On the other hand, a delivery port  912  has a constant outer diameter and a taper  912   a  where the inner diameter gradually increases toward the distal end. When the nozzle  911  is moved downward toward the delivery port  912 , the distal end of the nozzle  911  is inserted into the taper  912   a  of the delivery port  912 . The taper  911   a  of the outer side surface of the nozzle  911  and the taper  912   a  come into contact with each other and are sealed. In this case, the leakage of a contamination substance to the outside, which is presumed for the structure shown in  FIG. 74A , does not occur. Hence, the problem of contamination is not posed. 
     However, alignment between the delivery port  912  and the nozzle  911  must be very strictly done. When even a slight axial shift is present between the delivery port  912  and the nozzle  911 , no sufficient sealing can be ensured between the inner wall of the delivery port  912  and the nozzle  911 . Hence, leakage occurs, and as a consequence, solution supply cannot be done as specified, 
     When the combination of the nozzle  708  and delivery port  753  shown in  FIG. 55B  is employed for the combinations shown in  FIGS. 74A to 74C , the problem is not posed. 
     The nozzle  708  has a central axis  708   d  and an inner wall  708   e  which has a predetermined inner diameter and is separated from the central axis  708   d  by a predetermined distance. The nozzle  708  also has a nozzle lower surface  708   c  which is almost flat and almost perpendicular to the central axis  708   d . The outer diameter of the outer wall of the nozzle  708  is almost constant. 
     The delivery port  753  has a central axis  753   d  and an inner wall  753   c  which has a predetermined inner diameter and is separated from the central axis  753   d  by a predetermined distance. The inner wall  753   c  has a taper  753   a  whose inner diameter gradually increases from a halfway portion to the distal end. The delivery port  753  also has a port upper surface  753   b  which is almost flat and almost perpendicular to the central axis  753   d . The outer diameter of the outer wall of the delivery port  753  is almost constant. As shown in  FIG. 55B , the inner diameter of the inner wall  708   e  of the nozzle  708  is almost equal to that of the inner wall  753   c  of the delivery port  753 . The outer wall of the nozzle  708  and each of the outer walls of the delivery port  753  are also almost equal. 
     According to this structure, any liquid does not come into contact with the outer wall of the delivery port  753 . In addition, since the inner wall also has the taper  753   a , the biochemical solution does not leak to the outside and cause contamination. Even axial alignment between the delivery port  753  and the nozzle  708  requires not so strict accuracy. No problem of sealing is posed in the range where the port upper surface  753   b  and nozzle lower surface  708   c  sufficiently come into contact. Hence, solution supply is performed as specified. Furthermore, the inner wall  753   c  of the delivery port  753  has a tapered shape at the distal end portion. Even when a sample is injected using the pipette  791 , the pipette  791  can be smoothly inserted without making its tip hit or come into contact with any other portion. For this reason, the problem of unnecessary contamination or the like is not posed. 
       FIG. 55B  shows the combination of the nozzle  708  and delivery port  753 . This also applies to the combination of the nozzle  707  and introduction port  752 . In the combination of the nozzle  707  and introduction port  752 , the nozzle  707  is not used for the sample injection operation. Hence, the introduction port  752  shown in  FIG. 50  may be combined with the structure shown in  FIG. 54B . Alternatively, the introduction port  752  shown in  FIG. 50  may be combined with the nozzle  707  shown in  FIG. 54D . 
     The outline of an automatic analyzing operation using the base sequence automatic analyzing apparatus  700  according to this embodiment will be described with reference to the flow chart shown in  FIG. 72 . 
     First, data and conditions are input on the operation window of the computer  16  (s 11 ). Next, a sample is injected into the delivery port  753  of the cassette  703  by using the pipette  791  in the way shown in  FIG. 55A  (s 12 ). The seal  750  adhered to the outer surface  741  of the cassette bottom cover  712  of the cassette  703  is peeled (s 13 ). When the seal  750  is peeled after sample injection, the biochemical solution can be prevented from erroneously dropping to the connection port of the electric connector  730  to cause a short circuit at the time of sample injection. Hence, any operation error can be prevented. 
     Next, as shown in  FIG. 56 , in a tray open state wherein the slide stage  702   a  is open, the cassette  703  is loaded on the cassette loading groove  792  (s 14 ). The button of the slide operation button  704   a  is pressed to accommodate the cassette  703  in the housing  701  to set a tray closed state (s 15 ). Simultaneously with the accommodation operation, the valve unit/probe unit driving mechanisms  706   a  and  706   b  automatically drive the nozzles  707   a  and  708   a  an probe unit  710 . With this operation, the nozzles  707   a  and  708   a  are pressed against the introduction port  752  and delivery port  753  so that the ports and nozzles are sealed so as not to cause liquid leakage or air leakage (s 16 ). As a result, a closed channel is ensured between the nozzles  707   a  and  708   a  and the introduction port  752  and delivery port  753 . Simultaneously, electrical contact between the electric connectors  730  and the pads  762  and  763  is ensured. 
     Preparation for analysis is thus done. A start instruction is input by pressing a start button on the operation window of the computer  16  (s 17 ). 
     Upon receiving the start instruction, the control mechanism  15  executes measurement preparation processing (s 18 ). The measurement preparation processing will be described later in detail. When measurement preparation processing is ended, the control mechanism  15  controls the constituent elements of the measurement system  12 , solution supply system  13 , and temperature control mechanism  14  on the basis of instructions from the computer  16  to execute a series of measurement operations such as hybridization, cleaning, and signal detection (s 19 ). When the measurement is ended, the measurement result is transmitted from the control mechanism  15  to the computer  16  and analyzed. The analysis result is displayed on the display section of the computer  16 , and the processing is ended (s 20 ). The measurement and analyzing operations are the same as those of the first embodiment, and a detailed description thereof will be omitted. 
       FIG. 70  is a flow chart showing an example of measurement preparation processing (s 18 ). The measurement preparation processing (s 18 ) shown in  FIG. 70  can be executed before the measurement operation in (s 19 ) and, for example, before (s 17 ) (e.g., before (s 14 )). 
     First, the button of the slide operation button  704   a  is pressed to pull out the slide stage  702   a  and set the tray open state (s 181 ). The cassette  703  is loaded (s 14 ) and accommodated to set the tray closed state (s 182 ). Upon detecting the tray closed state by, e.g., the driving operation of the stage driving mechanism  891 , the control mechanism  15  determines the presence/absence of the cassette on the basis of the switching signal of the microswitch  811  (s 183 ). If it is determined that no cassette is present, an alert is turned on the display section  893  (s 184 ). The stage driving mechanism  891  is driven to slide the slide stage  702   a  or  702   b  to set the tray open state (s 185 ). A cassette re-load instruction is displayed on the display section  893  (s 186 ). 
     When it is determined by cassette determination (s 183 ) that a cassette is present, the control mechanism  15  determines the presence/absence of a seal (s 187 ). The presence/absence of a seal is determined by causing the detection light irradiation means  812  to emit detection light and determining whether the detection light can be detected by the detection photosensor  813 . If the seal is kept unpeeled, i.e., if the detection light is not detected, the flow advances to (s 184 ) to display an alert. The tray open state is set (s 185 ), and a cassette re-load instruction is displayed (s 186 ). In this case, a seal peeling instruction is preferably displayed together. 
     When the seal has been peeled, i.e., when the detection light is detected by the detection photosensor  813 , the valve unit/probe unit driving mechanism  706   a  or  706   b  is driven to move the nozzles  707   a  and  708   a  or  707   b  and  708   b  downward and also move the electric connectors  730  downward to align them to the cassette  703  (s 188 ). 
     The control mechanism  15  detects the detection signal from the electric connector  730 . It is determined on the basis of the detection signal whether the probe is in contact, i.e., whether each projecting electrode  703   a  of the electric connector  730  and a corresponding one of the pads  762  and  763  on the substrate  714  are properly in contact with each other, and electrical connection is properly ensured (s 189 ). 
     If it is determined that they are in contact, the measurement preparation processing (s 18 ) is ended, and measurement is started (s 19 ). If it is determined that they are not in contact, an alert is displayed (s 814 ). The tray open state is set (s 185 ), and a cassette re-load instruction is displayed (s 186 ). Together with the re-load instruction, a message representing that no satisfactory contact of the electric connectors  730  is obtained is displayed as a reason for re-load. Accordingly, the user can take measures by, e.g., cleaning the surface of the substrate  714 . 
     Although not illustrated in  FIG. 70 , when a sensor that detects stepwise the degree of press of the cassette type determination pin  789  is used to detect a plurality of types of cassettes, a cassette type determination step may be inserted between (s 183 ) and (s 187 ). In this case, the degree of press detected by the sensor is converted into data representing the type of cassette by the control mechanism  15  and displayed on the display section  893 . When it is confirmed before the start of measurement that the desired cassette  703  is set, any measurement using the cassette  703  of undesired type can be prevented. 
       FIG. 71  is a view for explaining an electrical connection presence/absence determination method in (s 189 ). As shown in  FIG. 71 , two pairs of pads  762  and pads  763  on the substrate  714  are short-circuited in advance in the substrate  714 . That is, a total of four pads are short-circuited in advance. The electric connectors  730  are moved downward to the substrate  714 . When the control mechanism  15  detects that a terminal A and a terminal B, and a terminal C and a terminal D on the side of the electric connectors  730  are short-circuited, the control mechanism  15  can determine that the electric connectors  730  and cassette  703  are properly electrically connected. To the contrary, when the control mechanism  15  cannot detect the short circuit between the terminal A and the terminal B or the short circuit between the terminal C and the terminal D, the control mechanism  15  can determine that no electrical contact is obtained between the electric connectors  730  and the cassette  703 . The probe units  710   a  and  710   b  and valve units  705   a  and  705   b  move together in the vertical direction. Hence, when the presence/absence of electrical connection is determined, it can be simultaneously confirmed whether the nozzles  707   a ,  707   b ,  708   a , and  708   b  and the introduction and delivery ports  752  and  753  obtain mechanical contact, i.e., are hermetically in tight contact with each other. 
     As described above, according to this embodiment, the series of measurement operations from hybridization to cleaning using buffers and electrochemical signal detection after an intercalating agent is added can be automatically and stably executed. 
     In this embodiment, the packing  713  integrated with solution injection and discharge ports is used. More specifically, on the side of the substrate  714 , a groove to form a linear channel is formed in correspondence with the array of electrodes on the surface of the substrate  714 . At two ends of the channel, the cylindrical introduction port  752  and delivery port  753 , which extend perpendicularly to the surface of the substrate  714 , are formed on the opposite side of the substrate  714 . A solution is injected/discharged into/from the introduction port  752  and delivery port  753 . The nozzles  707  and  708  of the valve unit  705  are attached to the introduction port  752  and delivery port  753  with good sealing properties. A biochemical solution or air is injected from the introduction port  752 . After the biochemical solution or air flows through the channel defined by the groove  758  between the packing  713  and the substrate  714 , the biochemical solution or air is discharged from the delivery port  753 . The delivery port  753  also serves as a sample injection port used to inject a sample onto the surface of the substrate  714 . As shown in  FIG. 55A , when a sample is to be injected using the pipette  791 , the tip of the pipette  791  is inserted into the delivery port  753 . When the pipette  791  is inserted, the distal end portion of the pipette  791  is sealed to the channel  756 , i.e., the inner wall or the delivery port  753 . After sealing, the sample in the pipette  791  is pushed out slowly. Accordingly, the sample in the pipette  791  is efficiently moved onto the substrate  714 . 
     In an arrangement different from this embodiment, i.e., when a flat packing is mounted on a substrate (chip), and a channel is formed in a cassette (chip cartridge), the channel in the cassette is long, and the amount of reagent is unnecessarily large. When a sample is injected into the cassette, the sample wastefully flows into unnecessary portions except the substrate because a long channel is present not only on the substrate but also in the cassette. In addition, the sealing properties between the cassette and the packing are poor. Leakage often occurs between the packing and the cassette, resulting in solution supply errors. When the arrangement of this embodiment is employed, the unnecessary amount of reagent decreases. In addition, since the sealing properties between the packing, the substrate, and the cassette become high, the stability of solution supply increases. 
     When the channel on the substrate is excessively large relative to the introduction and delivery ports, the pressure in the channel becomes lower than that in the ports. Hence, the biochemical solution easily comes to a boil, and bubbles are readily generated. The bubbles adversely affect the measurement. In this embodiment, the channel across the channel  756 , groove  758 , and channel  757  has an almost constant sectional area and an almost constant sectional shape. With this structure, the variation in pressure can be reduced, and boiling of the biochemical solution can be suppressed. Hence, the base sequence detection sensitivity becomes high. 
     When the valve unit  705  of this embodiment is used, the amount of reagent to be used for measurement can be minimized. For this reason, the running cost can be reduced. 
     More specifically, to introduce a reagent to an inspection portion such as a cassette or test tube, a metal needle or nozzle is often used. This is because a biochemical solution must be sucked or discharged by a needle that has pierced a rubber cap, and the needle is required to have a strength and durability to pierce the rubber. However, in detecting DNA or a base sequence, a metal needle cannot be used because metal ions cause detection errors. To the contrary, the valve unit  705  is made of PEEK or PTFE. The packing  713  is also made of silicone rubber or the like. They use no metal members. Hence, any detection error can be suppressed. 
     Normally, a port such as a needle or nozzle to the inspection portion and the valve that switches the reagent are connected by a tube. For this reason, a large amount of reagent exists in the tube that is not directly used for inspection. In addition, since the tube is manually attached, it is difficult to manage the length of the tube, and tube connection is unstable. As a result, the volume in the tube between valves may slightly change between apparatuses. Hence, the valve switching timing must be adjusted for each apparatus. That is, problems of an increase in reagent amount, an increase in instability of solution supply, and the necessity of valve switching timing adjustment are posed. However, when the valve unit  705  is used as in this embodiment, no tubes need be used between valves. Hence, the various problems caused by use of tubes can be solved. More specifically, the channel length can be decreased, and the necessary amount of reagent can greatly be reduced. Furthermore, since the capacity between valves can be held constant, the valve switching timing need not be adjusted for each apparatus, and solution supply stability increases. 
     As described above, when nozzles are made of a resin such as PEEK, and a manifold type valve unit in which the nozzles, valves, and pipes are integrated is used, the problems can be simultaneously solved. 
     With the valve unit  705  and cassette  703  of this embodiment, the data reproducibility can be increased. 
     In this embodiment, the measurement system  12 , solution supply system  13 , temperature control mechanism  14 , and control mechanism  15  are arranged in the housing  701  shown in  FIG. 35 . However, the present invention is not limited to this. For example, some of the measurement system  12 , solution supply system  13 , temperature control mechanism  14 , and control mechanism  15  may be arranged outside the housing  701 . Alternatively, the computer  16  may also be arranged in the housing  701 . 
     The bar code  744  is provided on the outer surface  741  of the cassette bottom cover  712 . However, the present invention is not limited to this. For example, the bar code  744  may be provided on the outer surface  721  of the cassette top cover  711 . 
     The channels  756  and  757  and groove  758  have almost the same sectional shape and sectional area. However, the present invention is not limited to this. For example, in all the channels  756  and  757  and groove  758 , the ratio of the sectional area of the thickest portion to that of the thinnest portion is preferably about 130% or less. 
       FIG. 55B  shows an example of the combination of the packing tip shape and nozzle tip shape. However, any combination of various modifications of the packing and nozzle tip shapes described above are available. Accordingly, the sealing properties between the packing and the nozzle can be increased. 
     As the materials of the nozzles  707  and  708  and valve bodies  781  and  782 , PEEK and PTFE are used. However, the present invention is not limited to this. For example, any one of PFA, PC, PMMA, PPS, PBT, and PCTFE may be used. Any other resin that can be deformed by pressurization can be applied. 
     The valve body  781  is indicated as a manifold having three valves or four valves, and the valve body  782  is indicated as a manifold having two valves, but the present invention is not limited to the number of the valves. A manifold having at least two valves or a structure having at least two valves communicating with the nozzles  707  and  708  can be used. 
     In the above embodiment, both the cassette  703  and the valve unit  705  are optimized. However, the present invention is not limited to this. For example, even when only the cassette  703  is optimized in the above-described way, and a conventional valve structure is used in place of the valve unit  705 , the effects of this embodiment can be obtained. Even when the valve unit  705  is optimized in the above-described way, and a conventional cassette (chip cartridge) is used in place of the cassette  703 , the effects of this embodiment can be obtained. 
     On the substrate  714 , the 3-electrode systems  761  each comprising a combination of a working electrode, counter electrode, and reference electrode are formed. However, the present invention is not limited to this. For example, as shown in  FIG. 7A ,  7 B,  10 , or  11 , counter electrodes and reference electrodes may be formed on the packing  713  while only working electrodes may be formed on the substrate  714 . 
     The ports  752  and  753  of the cassette  703  and the nozzles  707  and  708  are positioned by making a valve unit/probe unit driving mechanism  706  drive the valve unit  705 . However, the present invention is not limited to this. A cassette driving mechanism which drives and moves the cassette  703  relative to the valve unit  705  may be used in place of the valve unit/probe unit driving mechanism  706  as long as the mechanism can move the ports  752  and  753  relative to the nozzles  707  and  708 . 
     EXAMPLES 
     Example 1 
     An example in which SNPs detection is executed by using the base sequence detection apparatus according to the above-described first embodiment will be described below. The apparatus is applied to determine whether the SNPs base sequence of an MxA-88 gene is the G/G type, T/T type, or G/T hetero. 
     A DNA probe having a sequence complementary to the MxA gene is immobilized to the working electrodes  501  of the base sequence detection chip. Four kinds of probe DNA fragments whose bases at SNP positions are replaced with ATGC and DNA fragments (to be referred to as negative controls) having different sequences are immobilized to different electrodes (working electrodes  501 ). In this case, each probe with cysteine modified to an N terminus was spotted in 200 nL and left to stand for 1 hr, thereby immobilizing the probes to the working electrodes  501  made of Au. The printed board  22  in which the base sequence detection chip  21  prepared in the above way is attached to the chip cartridge  11 . 
     Next, DNA as a target whose base at the SNP position is G type is dissolved in 2×SSC-1 mmol/L EDTA solution and injected from the sample injection port  119  into the cell  115  by using a pipette or the like. The sample solution flows from the sample injection port  119  on the side of the delivery port  116   b  to the side of the introduction port  116   a  while filling the cell  115 . The outer surface of the introduction port  116   a  is formed in contact with the inner surface of the sealing member  24   a . For this reason, the cell  115  can be completely filled with the sample solution without forming any bubbles. 
     The chip cartridge  11  is attached to the apparatus main body (measurement system  12 , solution supply system  13 , and temperature control mechanism  14 ). When the apparatus program by the computer  16  is activated, all the subsequent processes are automatically executed. 
     The contents of automatic processing will be described. First, a reaction (hybridization) is caused at 45° C. for 15 min. After that, the solenoid valves and pump in the solution supply system  13  are controlled to supply the 0.2×SSC-1 mmol/L EDTA solution into the cell  115 . The state wherein the cell  115  is filled with the solution is held at 55° C. for 30 min. Nonspecific absorption DNA that has thus absorbed to the electrodes  211  and  212  having different layouts on the base sequence detection chip  21  is cleaned. Next, 10 μmol/L Hoechst 33258 solution is supplied into the cell  115 . In the state wherein the cell  115  is filled with the solution, an oxidation current from the Hoechst 33258 at each working electrode  501  is measured by the measurement system  12 . 
     Subsequently, the computer  16  extracts a region corresponding to the oxidation current of Hoechst from the current/voltage characteristic curve by the analysis program and derives the peak current value for each electrode (working electrode  501 ). In addition, the computer  16  executes statistical processing such as type determination filtering in accordance with the algorithm of the analysis program, thereby determining the type of the target DNA. The obtained determination result is displayed on the display of the computer  16 . As a result, it was determined that the signal intensity from an electrode corresponding to a probe whose probe sequence was C type was highest, and the base sequence at the SNP position of the target DNA was G type. 
     The uniformity of current values for electrodes of the same type in the plane of the base sequence detection chip  21  was 5% or less as a CV value. As a result, the SNPs detection reliability increased as compared to the conventional method. 
     Example 2 
     An example in which SNPs detection is executed by using the base sequence detection apparatus according to the above-described second embodiment will be described below. The apparatus is applied to determine whether the SNPs base sequence of an MxA-88 gene is the G/G type, T/T type, or G/T hetero. 
     A DNA probe having a sequence complementary to the MxA gene is immobilized to the working electrodes of the substrate  714 . Four kinds of probe DNA fragments whose bases at SNP positions are replaced with ATGC and DNA fragments (to be referred to as negative controls) having different sequences are immobilized to different working electrodes. In this case, each probe with cysteine modified to an N terminus was spotted in 200 nL and left to stand for 1 hr, thereby immobilizing the probes to the working electrodes made of Au. The thus prepared substrate  714  is attached to the cassette  703 . 
     Next, DNA as a target whose base at the SNP position is G type is dissolved in 2×SSC-1 mmol/L EDTA solution and injected from the introduction port  752  into the channel (cell) defined by the groove  758  and substrate  714  by using the pipette  791 . 
     The cassette  703  is placed on the slide stage  702  and accommodated in the housing  701 . When the apparatus program by the computer  16  is activated, all the subsequent processes are automatically executed. 
     The contents of automatic processing will be described. First, a reaction (hybridization) is caused at 45° C. for 15 min. After that, the solenoid valves and pump in the solution supply system  13  are controlled to supply the 0.2×SSC-1 mmol/L EDTA solution into the cell. The state wherein the cell is filled with the solution is held at 55° C. for 30 min. Nonspecific absorption DNA that has thus absorbed to the electrodes having different layouts on the substrate  714  is cleaned. Next, 10 μmol/L Hoechst 33258 solution is supplied into the cell. In the state wherein the cell is filled with the solution, an oxidation current from the Hoechst 33258 at each working electrode is measured by the measurement system  12 . 
     Subsequently, the computer  16  extracts a region corresponding to the oxidation current of Hoechst from the current/voltage characteristic curve by the analysis program and derives the peak current value for each working electrode. In addition, the computer  16  executes statistical processing such as type determination filtering in accordance with the algorithm of the analysis program, thereby determining the type of the target DNA. The obtained determination result is displayed on the display of the computer  16 . As a result, it was determined that the signal intensity from an electrode corresponding to a probe whose probe sequence was C type was highest, and the base sequence at the SNP position of the target DNA was G type. 
     The uniformity of current values for electrodes of the same type in the plane of the substrate  714  was 3% or less as a CV value. As a result, the SNPs detection reliability increased as compared to the conventional method. 
     As described above in detail, according to the embodiments, the uniformity of electrochemical reaction characteristics increases, and the detection reliability increases. 
     In addition, since a whole process including base sequence detection and analysis of detected data can be automatically executed, the data or measurement reproducibility increases. 
     As has been described above, the present invention is effective in the technical field of the base sequence detection apparatus which detects a base sequence and the technical field of the base sequence automatic analyzing apparatus which detects a base sequence.