Abstract:
The present invention aims at offering: a syringe connectable to a port in a fixed manner as well as capable of demonstrating high operational performance even in the case of direct connection where a connector is not used; a connector used for the syringe; and a syringe able to attach the connector thereto. For the attainment of the above objectives, the medical syringe of the present invention is a medical syringe including a cylindrical connection supporting member which enhances the holding force of a luer part inserted into a port when the medical syringe is connected to the port. The connection supporting member is set by sliding along the luer or a syringe body in a state of being movable between a first position near a tip of the luer and a second position away from the tip of the luer. The medical syringe is characterized in that, when the connection supporting member is moved to the second position, the tip of the luer part is exposed.

Description:
[0001]    This application is a divisional of application Ser. No. 11/547,055, filed Oct. 2, 2006, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a connector-attached syringe, a connector used for a syringe and a syringe. 
         [0004]    2. Background 
         [0005]    In the medical field, syringes (i.e., medical instruments for injection) are used in a variety of different ways. 
         [0006]    For example, in a typical syringe, a female taper connector, such as a needle hub having a needle tube, is generally attached to a luer part located at the tip of syringes, and such syringes are used to draw blood from patients and to inject medication held in the syringes to patients. 
         [0007]    In addition, syringes may be used in a system referred to as a pipeline system, such as a transfusion line system and a blood collection line system. In the pipeline system, a syringe is connected to an external port of the line system, and then medication in the syringe is applied therefrom, or reversely fluid is drawn from the line. To connect a syringe to such a line system, a direct connection method (also known as luer slip) and a fixed connection method are used. In the direct connection method, the luer part is inserted directly into the port of the line system. In the fixed connection method, a luer part  1141 L of a syringe  1000 L is connected to a port  1200 L by screwing them together using a connector (locknut)  1130 L, as shown in  FIGS. 41A to 41C . 
         [0008]    Prefilled syringes are also used in medical practices. Prefilled syringes are syringes containing prefilled medication in the syringe body. In this case, the nozzle tip of the syringe body is sealed by resin, for example, and the tip is opened before use and a plunger is inserted into the opening to thereby discharge the medication. Such prefilled syringes facilitate a rapid procedure by reducing the trouble and time required for administration of medication to patients and medication mixing. 
         [0009]    As to syringes connectable to the port of the above-mentioned line system in a fixed manner (referred to as luer-lock syringes), it is often the case that a locknut is already attached to the luer part. A stepped portion, whose diameter is different from that of the rest of the luer part, is provided in the luer part. The luer part is preliminarily inserted into the locknut, which is kept in place by the stepped portion. This structure is adopted in order to reliably connect the syringe and the line system and enable a quick connection operation. 
         [0010]    However, such a connector-attached syringe has a problem that the luer part cannot be connected to the direct connection port since the locknut is in the way, as shown in  FIG. 42 . 
         [0011]    Another problem is that, when attempting to attach a needle hub to the connector-attached syringe at the luer part, the user cannot see the right positional relationship between the luer part and the needle hub since the lock nut is in the way, as shown in  FIG. 43 , and cannot connect the luer part and needle hub successfully. In addition, since the locknut is set on the luer part, the length of a portion of the luer part exposing outside is insufficient, which leads to a problem of not being able to make the needle hub adequately hold onto the luer part. 
         [0012]    Thus, immediate improvement is desired in the versatility of locknut-attached syringes due to the requirements for speedy and accurate responses in medical field. 
       SUMMARY OF THE INVENTION 
       [0013]    One Embodiment of the present invention includes: a syringe connectable to a port in a fixed manner as well as capable of demonstrating high operational performance even in the case of direct connection where a connector is not used; a connector used for the syringe; and a syringe able to attach the connector thereto. 
         [0014]    In order to solve the above problems, one embodiment of the present invention is a connector-attached syringe having a connector for connecting a syringe unit to a port. The connector is disposed at a luer part in the syringe unit which includes a syringe body and a plunger. Here, the luer part includes an engaging portion for engaging with the connector. The connector includes a first opening for engaging with the engaging portion in the syringe axial direction and a second opening larger than the first opening and allowing for the luer part to be freely insertable and removable thereto and from in the syringe axial direction. The first and second openings communicate with each other. In some embodiments, the first and second openings may communicate with each other via a passage. 
         [0015]    Furthermore, in the present invention, the engaging portion may be a step positioned between a tip and a base of the luer part. 
         [0016]    First, according to such structures of the present invention, the luer part is inserted into the second opening (insertion hole) of the connector, and then slid into the first opening (engaging hole) so that the base side of the luer part next to the engaging portion is fitted into the engaging hole of the connector, and whereby the connector is attached to the syringe while these two are engaged with each other. Thus, the user is able to attach the connector to the syringe and connect the syringe, using the connector, to a fixed connection port of a transfusion line system or the like. 
         [0017]    Second, in one embodiment, the connector can be readily detached from the luer part engaged with the engaging hole of the connector by relatively moving the luer part to the insertion hole. 
         [0018]    Thus, the connector can be detached from the luer part so as not to be in the way when the luer part is connected to the direct connection port. As a result, the luer part can be reliably connected to a direct connection port of a transfusion line system or the like where a connector is not used. Thus, the syringe of the present invention exhibits high versatility. 
         [0019]    A prefilled syringe having a conventional structure has problems regarding operational performance such as the connector obstructing the view of the user, thus making it difficult to determine the positioning of the luer part and the needle hab. Additionally, the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the connector. However, the present invention is able to fundamentally solve these conventional problems since the connector is readily detachable from the connector. 
         [0020]    Additionally, in one embodiment, the passage is provided between the first and second openings so that these openings communicate with each other. Herewith, the luer part is forcedly shifted through the passage and moved to the engaging hole to be thereby reliably fitted when the syringe is used. 
         [0021]    To solve the above problems, one embodiment of the present invention is also a connector-attached syringe having a connector for connecting a syringe unit to a port. The connector is disposed at a luer part in the syringe unit which includes a syringe body and a plunger. Here, a first engaging portion for engaging with a second engaging portion on the connector is disposed on the outer peripheral surface of the syringe body. When an external force is applied, according to a predetermined operation, to one of the connector and the syringe unit in a direction different from a syringe axial direction, the engagement of the first and second engaging portions is released. 
         [0022]    Here, the first engaging portion may be, on the outer peripheral surface of the body of the syringe, a tip portion of the luer part, which has a larger diameter than the remaining portion (a stepped region in which a convex and a concave portions are provided side by side). 
         [0023]    Specifically, a body of the connector may be tubular, and the second engaging portion may be on an extension portion which extends from the body of the connector. Here, the first and second engaging portions are engaged with each other by inserting the luer part into the body of the connector and elastically contacting the extension portion with the outer peripheral surface of the syringe body. The engagement is released when the second engaging portion is detached from the outer peripheral surface by performing the predetermined operation on one of the connector and the syringe unit. 
         [0024]    First, according to such a structure of the present invention, the connector can be attached to the syringe while these two are engaged with each other by inserting the luer part into the connector and engaging the second engaging portion of the connector with the first engaging portion of the body of the syringe. Thus, the user is able to engage the connector with the syringe and connect the syringe, using the connector, to a fixed connection port of a transfusion line system or the like. 
         [0025]    Second, in one embodiment of the present invention, an external force is applied to the connector in a direction different from the syringe axial direction (e.g. in the syringe radial direction) according to a predetermined operation to detach the second engaging portion of the connector provided, for example, on the extention portion from the first engaging portion on the syringe. Herewith, the first and second engaging portions are disengaged, and whereby the connector can be readily detached from the luer part. 
         [0026]    Thus, the connector can be detached from the luer part so as not to be in the way when the luer part is connected to the direct connection port. As a result, the luer part can be reliably connected to a direct connection port of a transfusion line system or the like where a connector is not used. Thus, the syringe of the present invention exhibits high versatility. 
         [0027]    A prefilled syringe having a conventional structure has problems regarding operational performance such as that the connector obstructs the view of the user and makes it difficult to determine the positioning of the luer part and the needle hab and that the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the connector. However, embodiments of the present invention are able to fundamentally solve these conventional problems since the connector is readily detached from the connector. 
         [0028]    To solve the above problems, embodiments of the present invention are also a connector-attached syringe having a connector attached to a luer part jutting out from a syringe unit which includes a syringe body and a plunger. The connector is used for fixedly holding the syringe unit on a port. Here, the luer part includes an engaging portion for engaging with the connector. The connector includes a tubular body portion with a base and a constraint portion encircling a periphery of the body portion and exerting constraint effects on the base by shifting in the axial direction of the body portion. The base includes a plurality of swingable petal-shaped members. In a first state where the petal-shaped members are closed due to the constraint effects exerted on the base, the engaging portion is engaged with the petal-shaped members in the axial direction. In a second state where the petal-shaped members are open due to the base being free from the constraint effects, the luer part is freely insertable and removable into and from the connector in the axial direction via an open hole formed in a substantially central region of the base when the petal-shaped members are open. 
         [0029]    As to embodiments of the present invention, the constraint portion may be a nut having a screw on an internal peripheral surface thereof. Here, the body portion is in the shape of a substantial cylinder, and has a screw, which corresponds to the nut, on a section of the outer peripheral surface of the cylinder. The section is a range where the constraint portion is movable. In the first state, part of the body portion corresponding to the section is closed, taking on a shape of a cylinder. In the second state, the part of the body portion is open, spreading like open tweezers towards the base in the axial direction. 
         [0030]    Here, in the connector-attached syringe, the luer part may have, on the base side thereof, a reduced-diameter section, and the engaging portion may be a step created by the reduced-diameter section. 
         [0031]    Furthermore, one embodiment of the present invention is a connector for fixedly holding a syringe unit on a port and being disposed at a luer part jutting out from the syringe unit which includes a syringe body and a plunger. The connector comprises: a tubular body portion with a base; and a constraint portion encircling a periphery of the body portion and exerting constraint effects on the base by shifting in the axial direction of the body portion. Here, the base of the body portion includes a plurality of swingable petal-shaped members. In a first state where the petal-shaped members are closed due to the constraint effects exerted on the base, the luer part is engaged with the petal-shaped members in the syringe axial direction. In a second state where the petal-shaped members are open due to the base being free from the constraint effects, the luer part is freely insertable and removable into and from the connector via an open hole formed in a substantially central region of the base when the petal-shaped members are open. 
         [0032]    In the connector above, the constraint portion may be a nut having a screw on an internal peripheral surface thereof. Here, the body portion is in the shape of a substantial cylinder, and has a screw, which corresponds to the nut, on a section of the outer peripheral surface of the cylinder. The section is a range where the constraint portion is movable. In the first state, part of the body portion corresponding to the section is closed, taking on a shape of a cylinder, and in the second state, the part of the body portion is open, spreading like open tweezers towards the base in the axial direction. 
         [0033]    One embodiment of the present invention is also a procedure method for treatment and diagnosis using the connector-attached syringe above. 
         [0034]    With the connector-attached syringe of embodiments of the present invention, the connector can readily change the state between the first and the second states. Accordingly, the connector-attached syringe is capable of engaging the luer part of the syringe with the petal-shaped members of the base as well as making the luer part freely insertable and removable via the open hole on the base. That is, the connector-attached syringe allows for a selective use of the syringe between the luer-lock type and the luer-slip type according to the connection style of a port on which the syringe is to be fixedly held. 
         [0035]    As to the connector-attached syringe of embodiments of the present invention, the connector can be thus freely attached and detached according to the connection style of the port, and the detached connector can be used with another syringe. This results in a reduction in the cost burden on the user but does not cause a decrease in work performance when the syringe is used. In addition, the connector-attached syringe of the present invention can be connected to a port in either the luer-slip style or the luer-lock style, having high versatility for connection with a port. 
         [0036]    Since having the same structure as the connector attached to the luer part in the connector-attached syringe above, the connector of one embodiment of the present invention also has similar advantageous effects as described above. 
         [0037]    Therefore, the connector in one embodiment of the present invention is effective to enhance the versatility of the syringe when it is fixedly held on a port. 
         [0038]    Furthermore, one embodiment of the present invention is a connector-attached syringe having a connector attached to a luer part jutting out from a syringe unit which includes a syringe body and a plunger. The connector is used for fixedly hold the syringe unit on a port. Here, the luer part includes an engaging portion for engaging with the connector. The connector includes a plurality of components, which individually have interlocking members for coupling mechanisms. The interlocking members are interlocked with each other to thereby couple the components and make the connector in the shape of a tube having a base. When made in the shape of the tube, the connector engages with the engaging portion of the luer part. When the coupling of the components is released, the luer part is freely insertable and removable into and from the connector. 
         [0039]    As to the present invention, in the above-mentioned connector-attached syringe, the components may be symmetrical to each other and have end portions facing to each other. Here, a cutout is disposed on each of the end portions. The cutouts face to each other to form an engaging hole, which engages with the engaging portion of the luer part. 
         [0040]    As to the present invention, in the above-mentioned connector-attached syringe, at least one of the coupling mechanisms may include a locking tab and a locked tab which interlock with each other when the components are coupled. 
         [0041]    As to the present invention, in one of the above-mentioned connector-attached syringes, the luer part may have, on a base side thereof, a reduced-diameter section, and the engaging portion may be a step created by the reduced-diameter section. 
         [0042]    Furthermore, one embodiment of the present invention has a connector for fixedly holding a syringe unit on a port and being disposed at a luer part jutting out from the syringe unit which includes a syringe body and a plunger. The connector comprises: a plurality of components, which individually have interlocking members for coupling mechanisms. The interlocking members interlock with each other to thereby couple the components and make the connector in the shape of a tube having a base. Here, when made in the shape of the tube, the connector engages with the luer part. When the coupling of the components is released, the luer part is freely insertable and removable into and from the connector. 
         [0043]    As to the present invention, in the above-mentioned connector, the components may be symmetrical to each other and have end portions facing to each other. Here, a cutout is disposed on each of the end portions, and the cutouts face to each other to form an engaging hole, which engages with an engaging portion of the luer part. 
         [0044]    As to the present invention, in the above-mentioned connector, at least one of the coupling mechanisms may include a locking tab and a locked tab which interlock with each other when the components are coupled. 
         [0045]    Furthermore, one embodiment of the present invention is a procedure method for treatment and diagnosis using the connector-attached syringe above. 
         [0046]    The connector-attached syringe of this embodiment of the present invention has a structure in which the connector is freely attachable and detachable to and from the luer part of the syringe simply by changing the state of the connector between the state where the multiple components are coupled to form the tube with a base and the state where the coupling is released. Accordingly, the connector-attached syringe allows for a selective use of the syringe between the luer-lock type and the luer-slip type according to the connection style of a port on which the syringe is to be fixedly held. 
         [0047]    Additionally, with the connector-attached syringe, the connector may be detached from the syringe after used or when not used, and then the detached connector may be used with another syringe. 
         [0048]    Herewith, the connector-attached syringe of the present invention reduces the cost burden on the user but does not cause a decrease in work performance when the syringe is used. In addition, the connector-attached syringe of the present invention can be connected to a port in either the luer-slip style or the luer-lock style, exhibiting high versatility for connection with a port. 
         [0049]    Similarly to the connector attached to the connector-attached syringe above, the connector of the present invention can be easily attached and detached to and from the luer part of the syringe simply by changing the state of the connector between the state where the multiple components are coupled to form the tube with a base and the state where the coupling is released. Herewith, the connector can be attachable and detachable according to need—for example, the connector is engaged with the luer part of the syringe when the syringe and port are connected in the luer-lock style, and the connector is disengaged when they are connected in the luer-slip style. 
         [0050]    As a result, the connector of the present invention is effective to enhance the versatility of the syringe for connection with a port. 
         [0051]    In order to solve the above problems, in one embodiment of the present invention is a connector-attached medical syringe having a tubular connection supporting member and a pin for increasing, when a syringe unit including a syringe body and a plunger is connected to a port, a connecting force between a luer part of the syringe unit and the port. The luer part is inserted into the port. Here, the connection supporting member includes a first insertion hole disposed on the outer peripheral surface thereof and a second insertion hole disposed on an end portion thereof. The first insertion hole is for the pin to be inserted thereto. The pin includes a fit portion for being fitted with the luer part. The syringe unit freely changes a state thereof between (i) a connector hold state, in which, when the luer part is inserted into the second insertion hole, the pin is inserted into the first insertion hole along an insertion path until the fit portion is fitted with the luer part and (ii) a connector release state, in which the fitting of the fit portion and the luer part is released by pulling the pin out from the first insertion hole. 
         [0052]    The syringe of the present invention may be a connector-attached medical syringe having a tubular connection supporting member and a pin for increasing, when a syringe unit including a syringe body and a plunger is connected to a port, a connecting force between a luer part of the syringe unit and the port. The luer part is inserted into the port. Here, the connection supporting member includes a first insertion hole disposed on the outer peripheral surface thereof and a second insertion hole disposed on an end portion thereof. The first insertion hole is for the pin to be inserted thereto. The pin includes a fit portion for being fitted with the luer part. The syringe unit freely changes a state thereof between (i) a connector hold state, in which, when the luer part is inserted into the second insertion hole, the pin is inserted into the first insertion hole along an insertion path until the fit portion is fitted with the luer part and (ii) a connector release state, in which the fitting of the fit portion and the luer part is released by pulling the pin out from the first insertion hole. 
         [0053]    Herewith, the syringe can be used as a so-called luer-slip syringe by pulling out the pin and thereby disengaging the connector from the syringe. In addition, the syringe can be used also as a so-called luer-lock syringe by inserting the pin into the connector and thereby engaging the luer part and the connector. 
         [0054]    That is, since the syringe functions as either type, its versatility increases. 
         [0055]    In addition, the luer part may be in the shape of a substantially cylinder locally having a reduced-diameter section in vicinity of a central region or a base portion thereof. Here, the insertion path of the pin is a line connecting facing sections on the outer peripheral surface and passing in vicinity of the central axis of the connection supporting member. The fitting is made when the fit portion is fitted with the reduced-diameter section of the luer part in the vicinity of the central axis. 
         [0056]    According to the structure, the central axis of the luer part coincides with or come close to that of the connector. 
         [0057]    As to a connection-target instrument in the luer-lock style, an insertion point for the luer part is generally located in the middle of an engaging structure such as a threaded portion or a groove portion for engagement. Therefore, since the central axes of the luer part and connector substantially coincide, the insertion of the luer part into the port can be performed while the pin is being fitted with the luer part. 
         [0058]    In addition, the fitting may be made so that the pin is freely rotatable around the central axis of the reduced-diameter section. 
         [0059]    Accordingly, the syringe and the connection-target instrument in the luer-lock style can be connected and fixed to each other simply by rotating the connector without rotating the syringe itself. 
         [0060]    In addition, the pin may include a handle portion to be grasped in a case of insertion and pullout. This facilitates easy insertion and pullout of the pin. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0061]      FIG. 1  is a cross sectional view showing a structure of a prefilled syringe of Embodiment 1; 
           [0062]      FIG. 2  shows the way to attach a locknut of Embodiment 1 to the prefilled syringe; 
           [0063]      FIG. 3  shows the prefilled syringe of Embodiment 1 connected to a fixed connection port; 
           [0064]      FIG. 4  shows the prefilled syringe of Embodiment 1 connected to a direct connection port; 
           [0065]      FIG. 5  shows the prefilled syringe of Embodiment 1 to which a conventional needle hub is attached; 
           [0066]      FIG. 6  shows a structure of a locknut of Embodiment 2; 
           [0067]      FIG. 7  shows a structure of a locknut of Embodiment 3; 
           [0068]      FIG. 8  shows a structure of a locknut of Embodiment 4; 
           [0069]      FIG. 9  shows a structure of a locknut of Embodiment 5; 
           [0070]      FIG. 10  is a cross sectional view showing a structure of a prefilled syringe of Embodiment 6; 
           [0071]      FIG. 11  shows the way to attach a locknut of Embodiment 6 to the prefilled syringe; 
           [0072]      FIG. 12  shows the locknut of Embodiment 6 fitted to the prefilled syringe; 
           [0073]      FIG. 13  is a cross sectional view of the prefilled syringe and locknut of Embodiment 6; 
           [0074]      FIG. 14  is a cross sectional view showing the prefilled syringe of Embodiment 6 connected to a direct connection port of a transfusion line system; 
           [0075]      FIG. 15  is a cross sectional view showing a luer part of the prefilled syringe of Embodiment 6 to which a needle hub is attached; 
           [0076]      FIG. 16  shows a structure of a locknut and a prefilled syringe of Embodiment 7; 
           [0077]      FIG. 17  shows a structure of a locknut and a prefilled syringe of Embodiment 8; 
           [0078]      FIG. 18  shows a structure of a locknut and a prefilled syringe of Embodiment 9; 
           [0079]      FIG. 19  is a cross sectional view showing a prefilled syringe and a locknut of Embodiment 10; 
           [0080]      FIG. 20  is an assembly drawing of the prefilled syringe, a fixture and the locknut of Embodiment 10; 
           [0081]      FIG. 21  shows the way to connect the prefilled syringe of Embodiment 10 to the fixed connection port; 
           [0082]      FIG. 22  shows the state of the locknut being disengaged from the fixture of Embodiment 10; 
           [0083]      FIG. 23  shows the prefilled syringe of Embodiment 10 connected to the direct connection port; 
           [0084]      FIG. 24  shows the prefilled syringe of Embodiment 10 to which a conventional needle hub is attached; 
           [0085]      FIG. 25  shows a structure of a locknut of Embodiment 11; 
           [0086]      FIG. 26  shows a structure of a locknut of Embodiment 12; 
           [0087]      FIG. 27A  is a lateral side view (with a partial cross sectional view) of a connector  1  of Embodiment 13; and  FIG. 27B  is a front view of the connector  1 ; 
           [0088]      FIG. 28A  is a lateral side view (with a partial cross sectional view) of the connector  1  before the connection with a syringe  5  of Embodiment 13; and  FIG. 28B  is a lateral side view (with a partial cross sectional view) of the connector  1  after the connection with the syringe  5  of Embodiment 13; 
           [0089]      FIG. 29  is a perspective view showing a relation between the connector  1  and an extension tube  6  when they are to be connected to each other, according to Embodiment 13; 
           [0090]      FIG. 30  is a lateral side view showing a coinfusion port  7  or an injection needle is to be connected to the syringe  5 J in luer-slip style without using the connector  1 , according to Embodiment 13; 
           [0091]      FIG. 31A  is a perspective view of a connector  1  of Embodiment 14; and  FIG. 31B  is a front view of the connector  1 ; 
           [0092]      FIG. 32  is a perspective view showing a relationship between the connector  1  and an extension tube  6  when they are to be connected to each other, according to Embodiment 14; 
           [0093]      FIG. 33  is a lateral side view showing a coinfusion port  7  or an injection needle  8  is to be connected to the syringe  5 K in the luer-slip style without using the connector  1 , according to Embodiment 14; 
           [0094]      FIG. 34  is a perspective view showing a relation between a connector  2  of Embodiment 15 and the syringe  5 ; 
           [0095]      FIG. 35  is a perspective view showing a shape of a connector  3  of Embodiment 16; 
           [0096]      FIG. 36  illustrates usage of a syringe according to Embodiment 17; 
           [0097]      FIG. 37  shows the way of a coupling pin being inserted into a lock part according to Embodiment 17; 
           [0098]      FIG. 38  shows the way of the syringe of Embodiment 17 being inserted into a coinfusion port in the luer-slip style; 
           [0099]      FIG. 39  shows an example of realizing a lock mechanism of a syringe of Embodiment 18, using another structure other than a screw nut; 
           [0100]      FIG. 40  shows an example where the lock part and syringe are engaged with each other using a coupling pin of Embodiment 19, the shape of which is different from that of the coupling pin of Embodiment 17; 
           [0101]      FIG. 41  illustrates usage of a conventional luer-lock syringe; 
           [0102]      FIG. 42  shows a structure of a conventional locknut and a prefilled syringe; and 
           [0103]      FIG. 43  shows a structure of a conventional locknut and a prefilled syringe. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0104]    The following sequentially describes Embodiments 1 through 19 of medical syringes of the present invention with the aid of drawings. 
       1. Embodiment 1 
     1-1. Overall Structure of Prefilled Syringe 
       [0105]      FIG. 1  is a cross sectional diagram showing structures of a prefilled syringe and a connector (a locknut) according to Embodiment 1. Note that, here, a structure is adopted in which a prefilled syringe and a locknut are combined, however, the present invention may be applied to syringes other than prefilled syringes. For convenience of explanation, a plunger  40  is shown here in normal lateral view rather than in cross section. 
         [0106]    As shown in  FIG. 1 , a prefilled syringe  1  may comprise a syringe body  10 , the plunger (also referred to as a piston)  40  and the like. 
         [0107]    In this embodiment, the syringe body  10  is a tubular body formed by injection molding a material with high chemical resistance, such as polyethylene, polypropylene, polycarbonate or polyvinyl chloride. The tip end of the syringe body  10  is sealed by a top face portion  110 , and a luer part  120  juts or extends out from the center of the top face portion  110 . 
         [0108]    On the other hand, an opening  12  may be formed at the posterior end of the syringe body  10 . Although the luer part  120  is formed by drawing to basically give a tapered shape, a stepped portion  123  is provided in a part of the tapered shape, which thereby forms a luer base portion  121  having a smaller diameter and a luer tip portion  122  located on the tip side of the luer part  120  having a larger diameter. 
         [0109]    A locknut  30 , to be hereinafter described, may be fitted to the stepped portion  123 . In addition, the luer tip portion  122  may be formed in a tapered shape in compliance with ISO6/100 so that the regular needle hub  20  can be attached easily. In  FIG. 1 , a cap  20  is attached to the tip of the luer part  120 . 
         [0110]    In the following description, the longitudinal direction of the syringe body  10  is referred to as an “axial direction” while a direction perpendicular to the axial direction is referred to as a “radial direction”. 
         [0111]    The plunger  40  can be made of a resin material with high chemical resistance, similarly to the syringe body  10 , and includes a plunger body  42  having a cruciform cross sectional shape for the purpose of reinforcement, at each end of which are formed disk-shaped end pieces having main surfaces in the radial direction. One of the end pieces is a pressing end portion  41  to be pressed by the user with a thumb, and the other end piece is a head portion  43  that is inserted inside the syringe body  10  in the axial direction. 
         [0112]    A packing  44  is provided at the tip of the head portion  43  in a manner to make tight contact with the internal wall of the syringe body  10 . Here, medication  100  is held in the syringe body  10 , which is internally sealed by the packing  44  and the cap  20 . 
         [0113]    When using the prefilled syringe  1  having such a structure, the user removes the cap  20  to enable discharge of the medication  100 . As the user pushes the pressing end portion  41  of the plunger  40  into the syringe body  10  with a thumb, the medication  100  is discharged from the tip of the luer part  120  according to the depressed amount of the plunger  40 . 
       1-2. Structure of Locknut 
       [0114]    The prefilled syringe  1  of Embodiment 1 includes the locknut  30 , which is a connector easily detachable from the luer part  120 , and which is attached so as to engage, in the axial direction, with the stepped portion  123  of the luer part  120 . The locknut  30  is used in the medical field as a connection implement for connecting the prefilled syringe  10  to a fixed connection port of a transfusion line system or blood collection line system. 
         [0115]    The locknut  30  has a cylindrical form with a bottom, being formed by injection molding a resin material with high mechanical strength. A screw thread is cut on the internal surface of a lateral side portion  301 , which corresponds to the cylindrical part of the locknut  30 , to thereby form a female screw  3010  in compliance with, for example, ISO594-2. The female screw  3010  may engage with a male screw  5010  to be hereinafter described. 
         [0116]    A snowman-shaped hole  3020  formed by perforating two holes communicating with each other is provided on a main surface portion  302  that is the bottom of the locknut  30  (for detail, see  FIG. 2 ). One of these two holes is a loose-insertion hole  3021  and is formed on the main surface portion  302  away from the center by perforation. The other hole is an engaging hole  3022  which is formed in the center of the main surface portion  302  by perforation. The loose-insertion hole  3021  has a diameter at least larger than that of the luer tip portion  122  so that the entire luer part  120  of the prefilled syringe  1  can be inserted into the hole with clearance therebetween. On the other hand, the engaging hole  2022  has a diameter slightly smaller than that of the luer tip portion  122  so that the stepped portion  123  of the luer part  120  is fitted thereto and the locknut  30  rotates with respect to the luer part  120 . A passage  303  is formed between the loose-insertion hole  3021  and engaging hole  3022 , having a diameter further smaller than that of the engaging hole  3022 . The width of the passage  303  is slightly smaller than the diameter of the luer base portion  121  so that the luer part  120  shifts to the passage  303  side only when more than a certain amount of force is applied to the luer base portion  121 . 
       1-3. Engagement of Syringe and Locknut 
       [0117]      FIG. 2A  shows how to attach the locknut  30  to the syringe  1  and  FIG. 2B  shows the locknut  30  after the attachment. As to the locknut  30  having the above structure, when using the prefilled syringe  1 , the user first inserts the luer part  120  of the prefilled syringe  1  into the loose-insertion hole  3021  in the axial direction, as shown in  FIG. 2A  ( FIG. 2A  shows that the luer part  120  is about to be inserted in the direction A, i.e. the axial direction). Since the loose-insertion hole  3021  has a diameter sufficiently larger than that of the luer tip portion  122  of the luer part  120 , the luer part  120  can be smoothly inserted into the locknut  30 . 
         [0118]    In the second step after the user has inserted the luer part  120  into the loose-insertion hole  3021  so as to assuredly insert the luer base portion  121  thereto, the user brings the lateral side of the luer base portion  121  into contact with the lateral surface of the loose-insertion hole  3021  and shifts the luer part  120  to the engaging hole  3022  via the passage  303  ( FIG. 2A  also shows that the luer part  120  is to be shifted in the direction B). In this process, the luer base portion  121  is forcedly shifted through the passage  303 , then the stepped portion  123  shifts and becomes fitted into the small engaging hole  3022 . Since the diameter of the engaging hole  3022  matches that of the stepped portion  123  and the passage  303  exists between the engaging hole  3022  and loose-insertion hole  3021 , the stepped portion  123  of the luer part  120  abuts against the circumference of the engaging hole  3022  and is securely engaged in the axial direction, as shown in  FIG. 2B . 
         [0119]    After the locknut  30  having the snowman-shaped hole  3020  is engaged with the syringe body  10 , these two can be readily detached from each other in the following manner. That is, the user shifts the luer part  120  from the engaging hole  3022  to the insertion hole  3021  as exerting some force on the luer part  120 . This operation can be performed in a reversible and simple fashion (for example, in one hand), and the user is therefore able to easily attach the locknut  30  to the prefilled syringe  1  when required, and detach the locknut  30 , when not required, to thereby use the prefilled syringe  1  alone. 
         [0120]      FIG. 3  is a cross sectional view showing that the prefilled syringe  1  is connected, using the locknut  30 , to a fixed connection port  50  of a transfusion line system. As the male screw  5010  of the port  50  is screwed into the female screw  3010  of the locknut  30 , the luer tip portion  122  of the luer part  120  of the prefilled syringe  1  comes in close contact with a packing  52  provided inside the port  50 , and eventually gets inserted into the transfusion line while pressing the packing  52 . At this point, in the locknut  30 , the circumference of the engaging hole  3022  exerts pressure on the stepped portion  123  of the luer part  120  so that they tightly engage with each other. Thus, even if some degree of tension is applied to the prefilled syringe  1 , the prefilled syringe  1  does not come apart from the port  50  along the axial direction. As a result, the user is able to safely push the plunger  40  into the syringe body  10  accordingly and deliver a required amount of medication  100  to the inside of the port  50 . 
         [0121]    On the other hand,  FIG. 4  is a cross sectional view showing that the locknut  30  has been detached from the prefilled syringe  1 , which is then connected to a direct connection port  500  of a transfusion line system. Thus, according to Embodiment 1, since the locknut  30  has been taken off, or otherwise may be an obstacle, the luer tip portion  122  of the prefilled syringe  1  is properly and tightly held by the packing  52  in the port  500 , which makes a suitable connection between the prefilled syringe  1  and the port  500 . 
         [0122]      FIG. 5  is a cross sectional view showing that the locknut  30  has been detached from the prefilled syringe  1  and a needle hub  60  is attached to the luer tip portion  122 . The needle hub  60  has a structure in which a socket portion  61  composed of a resin material and formed to match the shape of the luer tip portion  122  holds a needle tube  62  which is an injection needle. With the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in  FIG. 43 , the locknut obstructs the view of the user and makes it difficult to determine the positioning of the luer part and the needle hub, thereby creating the danger of the user mistakenly pricking himself/herself and coming into contact with infectious material. In addition, the conventional problem that the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the locknut can be fundamentally solved by Embodiment 1 since the snowman-shaped hole  3020  enables easy detachment of the locknut  30  from the prefilled syringe  1 . 
       Other Embodiments 
       [0123]    Note that although in Embodiment 1 the snowman-shaped hole is formed by circular insertion and engaging holes communicating with each other via the passage, the following embodiments are also within the scope of the present invention. 
       2. Embodiment 2 
       [0124]    With a snowman-shaped hole  3020   a  in a locknut  30 A of Embodiment 2 shown in  FIG. 6 , arcs of a loose-insertion hole  3021   a  and an engaging hole  3022   a  are partially overlapped with each other, and two circumferences of these holes where they overlap form a passage  303   a.    
         [0125]    With the snowman-shaped hole  3020   a  having such a shape, the present invention is able to achieve an equivalent effect to that of Embodiment 1. In addition, since the passage  303   a  of Embodiment 2 is formed where the loose-insertion hole  3021   a  and engaging hole  3022   a  overlap, it is rather edged as compared with that of Embodiment 1, and the luer part  120  is reliably engaged with the engaging hole  3022   a  due to the shape. 
       3. Embodiment 3 
       [0126]    With a snowman-shaped hole  3020   b  in a locknut  30 B according to Embodiment 3 shown in  FIG. 7 , an engaging hole  3022   b  is formed between two insertion holes  3021   b A and  3021   b B. Although arcs of the engaging hole  3022   b  and each of the insertion holes  3021   b A and  3021   b B are partially overlapped with each other, these holes may be communicated with each other by passages therebetween. In addition, the insertion holes  3021   b A and  3021   b B need not have the same size and shape, but need to have sizes such that at least the stepped portion  123  of the luer part  120  can be inserted thereto with clearance therebetween. 
         [0127]    With the snowman-shaped hole  3020   b  having such a structure, the user can detach the locknut  30  easily when using the syringe  1  since the luer part  120  can be shifted from the engaging hole  3022   b  to either of the two insertion holes  3021   b A and  3021   b B. This results in reducing the operational load on the user. Embodiment 3 is expected to achieve a very high level of convenience especially in medical practices which require the user to handle the prefilled syringe  1  and locknut  30  in one hand based on the treatment method using the prefilled syringe  1 . 
       4. Embodiment 4 
       [0128]    With a snowman-shaped hole  3020   c  in a locknut  30 C of Embodiment 4 shown in  FIG. 8 , a circular engaging hole  3022   c  is communicated with a rectangular loose-insertion hole  3021   c  via a passage  3023   c.    
         [0129]    With such a structure also, a similar effect to that of the locknut  30  of Embodiment 1 can be achieved. An additional advantage is that the user readily recognizes and distinguishes the loose-insertion hole  3021   c  and engaging hole  3022   c  without confusion and is able to properly use the locknut  30 C since the shapes of these holes are distinctly different. 
       5. Embodiment 5 
       [0130]    With a snowman-shaped hole  3020   d  in a locknut  30 D of Embodiment 5 shown in  FIG. 9 , a circular engaging hole  3022   d  is communicated with a hexagonal loose-insertion hole  3021   d  via a passage  3023   d.    
         [0131]    With such a structure also, a similar effect to that of the locknut  30  of Embodiment 1 can be achieved. Similarly to Embodiment 4, since the shapes of the loose-insertion hole  3021   d  and engaging hole  3022   d  are distinctly different, the user readily recognizes and distinguishes these two holes without confusion and is able to properly use the locknut  30 D. 
       Additional Particulars Regarding Embodiments 1 Through 5 
       [0132]    Although the prefilled syringe  1  of the present invention has been explained with an example in which the needle hub  60  is attached after the locknut  30  being detached, the present invention is not limited to that case. Instead of a needle hub, a tubelike luer or a tube may be used. It is effective to attach, from the top, a cap or the like to the prefilled syringe  1  with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking. As such a cap, one similar to a cap for a vial container can be used. 
         [0133]    Each embodiment described above discloses a structural example of a connector (locknut) in which a screw thread is cut to form a female screw. However, the present invention is not confined to this structure, and the prefilled syringe  1  may be appropriately connected to the port of a line system using a discontinuous thread, a cup joint, or another structure. 
         [0134]    The luer part of the syringe used in the present invention does not necessarily have a circular cross section, and either one of the luer tip portion and the luer base portion or both have rectangular, elliptic, or triangle cross sections. Note however that it is preferable that the shape of the engaging hole be appropriately decided in accordance with the cross sectional shape of the stepped portion of the luer part so as to stably and reliably engage the luer part in the engaging hole of the locknut. 
       6. EMBODIMENT 6 
     6-1. Overall Structure of Prefilled Syringe 
       [0135]      FIG. 10  is a cross sectional view showing structures of a prefilled syringe and a connector (locknut) according to Embodiment 1. Note that Embodiment 6 has a structure in which a prefilled syringe and a locknut are combined, however, the present invention is applicable to syringes other than prefilled syringes. For convenience of explanation, the plunger  40  is shown here in normal lateral view rather than in cross section. 
         [0136]    The prefilled syringe  1  shown in the figure may comprise the syringe body  10 , the plunger (also referred to as a piston)  40  and the like. The syringe body  10  may be a tubular body formed by injection molding a material with high chemical resistance, such as polyethylene, polypropylene, polycarbonate or polyvinyl chloride. The tip end of the syringe body  10  is sealed by the top face portion  110 , and the luer part  120  formed by drawing to give a tapered shape juts or extends out from the center of the top face portion  110 . The luer part  120  is formed in a tapered shape in compliance with IS06/100 so that the normal needle hub  20  is easily attached thereto. In  FIG. 10 , the cap  20  is attached to the tip of the luer part  120 . The prefilled syringe  1  of the present invention is configured, such that convex portions  101  and  102  and a concave portion  103  are provided side by side, situated closer to the luer part  120 , so as to encircle the circumference of the syringe body  10 . These portions are for engaging with the locknut  30  to be hereinafter described. 
         [0137]    On the other hand, the opening  12  is formed at the posterior end of the syringe body  10 . 
         [0138]    In the following description, the longitudinal direction of the syringe body  10  is referred to as an “axial direction” while a direction perpendicular to the axial direction is referred to as a “radial direction”. 
         [0139]    The plunger  40  is made of a resin material with high chemical resistance, similarly to the syringe body  10 , and includes the plunger body  42  having a cruciform cross sectional shape for the purpose of reinforcement, at each end of which are formed disk-shaped end pieces having main surfaces in the radial direction. One of the end pieces is the pressing end portion  41  to be pressed by the user with a thumb, and the other end piece is the head portion  43  that is inserted inside the syringe body  10  in the axial direction. 
         [0140]    The packing  44  is provided at the tip of the head portion  43  in a manner to make tight contact with the internal wall of the syringe body  10 . Here, medication  100  is held in the syringe body  10 , which is internally sealed by the packing  44  and the cap  20 . 
         [0141]    When using the prefilled syringe  1  having such a structure, the user removes the cap  20  to enable discharge of the medication  100 . As the user pushes the pressing end portion  41  of the plunger  40  into the syringe body  10  with a thumb, the medication  100  is discharged from the tip of the luer part  120  according to the depressed amount of the plunger. 
       6-2. Structure of Locknut 
       [0142]    The prefilled syringe  1  of Embodiment 6 is configured, such that the locknut  30 , which is a connector easily detachable from the luer part  120 , is attached thereto as shown in  FIG. 10 . The locknut  30  is used in the medical field as a connection implement for connecting the prefilled syringe  10  to a fixed connection port of a transfusion line system or blood collection line system. 
         [0143]    The locknut  30  has a cylindrical shape having a bottom, and is formed by injection molding a resin material with high mechanical strength. A screw thread is cut on the internal surface of a lateral side portion  301 , which corresponds to the cylindrical part of the locknut  30 , to thereby form a female screw  3010  in compliance with, for example, ISO594-2. The female screw  3010  engages with the male screw  5010  to be hereinafter described. 
         [0144]    A rib  3020  having in the center a perforation with a size such that the luer part  120  can be inserted, leaving no space therebetween, is formed in the locknut  30 , and forms a bulkhead which divides the internal space of the locknut  30  into a syringe side and a port side. On the other hand, outside the locknut  30 , two plate-like arms  31  and  32  are formed parallel to the syringe body  10  in the axial direction to make T shapes with the rib. Tab projections  310  and  320  having triangular cross sections are formed on the inner sides of the tip ends of the arms  31  and  32 . The shape of the projections  310  and  320  is made to be complementary to that of the concave portion  103  of the syringe body  10 . 
       6-3. Detachment of Locknut from Syringe 
       [0145]      FIG. 11  shows the way of engaging the locknut  30  and the state of locknut  30  after the engagement. 
         [0146]    As to the locknut  30  having the above structure, when the prefilled syringe  1  is used, the user first inserts the luer part  120  into the locknut  30  (here, the luer part  120  is inserted in the center of the rib  3020  inside the locknut  30 ) as shown in  FIG. 11 . At this point, the user makes sure that the luer part  120  is inserted so that the rib  3020  comes all the way to the base of the luer part  120 . 
         [0147]    In the second step, using the arms  31  and  32  extending from the locknut  30 , the user engages the projections  310  and  320  provided on the inner sides of the arms  31  and  32  with the concave portion  103  of the syringe body  10  by elastically contacting and fitting them with each other. The shape of the projection  310  and  320  is formed so as to conform to the convex portions  101  and  102  and the concave portion  103 , and therefore the locknut  30  is securely kept on the syringe body  10  by the engagement. 
         [0148]      FIG. 12  is a cross sectional view showing the prefilled syringe  1  that is, using the locknut  30 , connected to the fixed connection port  50  of a transfusion line system. As the male screw  5010  of the port  50  is screwed into the female screw  3010  of the locknut  30 , the tip of the luer part  120  of the prefilled syringe  1  is tightly pressing the packing  52  provided inside the port  50 , and eventually gets inserted into the transfusion line. The prefilled syringe  1  is not disengaged while in use because the syringe body  10  is securely fixed with the locknut  30  by the convex portions  101  and  102 , concave portion  103 , and projections  310  and  320 , and besides the luer part  120  is supported by the rib  3020  in the locknut  30  to keep the luer part  120  in place. As a result, the user is able to safely push the plunger  40  into the syringe body  10  accordingly and deliver a required amount of medication  100  to the inside of the port  50 . 
         [0149]    According to Embodiment 6, after being engaged with the syringe body  10 , the locknut  30  can be easily disengaged from the syringe  1  by performing a predetermined operation in the following manner. This operation can be performed in a reversible and simple fashion (for example, in one hand), and the user is therefore able to easily engage the locknut  30  with the prefilled syringe  1  when required, and detach the locknut  30 , when not required, to thereby use the prefilled syringe  1  alone. 
         [0150]    In a specific method of disengaging the locknut  30  (the predetermined operation), the user presses the arms  31  and  32  on the anterior side of the syringe  1 , as shown in  FIG. 13 , which is a cross sectional view of the syringe  1  and locknut  30 . In this embodiment, “the principle of leverage” may be applied, with the centers of the arms  31  and  32  being fulcrums while the points where the projections  310  and  320  abut on the convex portions  101  being working points. Accordingly, the ends of the arms  31  and  32  where the projections  310  and  320  are provided warp away from the syringe body  10  (i.e. an external force is applied to the locknut  30  in a direction different from the syringe axial direction). Herewith, the projections  310  and  320  detach and come free, at least, from the convex portion  102  and concave portion  103 . While maintaining this state, the user is able to pull out the locknut  30  from the syringe  1  with a little force. Note that the locknut  30  can be easily disengaged from the syringe body  10  by spreading outward the ends of the arms  31  and  32  with the projections  310  and  320  by fingers, instead of pressing the arms  31  and  32  on the anterior side of the syringe  1 . 
         [0151]    It is desirable that the arms  31  and  32  be provided on the locknut  30  so that T shapes are formed with the rib, and points where the arms  31  and  32  abut on the rib become fulcrums. This, the user can easily disengage the locknut  30  from the syringe body  10  by pushing the posterior ends of the arms  31  and  32  to spread the anterior ends thereof. 
         [0152]      FIG. 14  is a cross sectional view showing that the prefilled syringe  1  may be connected to the direct connection port  500  of a transfusion line system after the locknut  30  has been detached therefrom according to the above method. Thus, in Embodiment 6, since the locknut  30  has been removed, or may otherwise be an obstacle, the luer part  120  of the prefilled syringe  1  is properly and tightly held by the packing  52  in the port  500 , which makes a suitable connection between the prefilled syringe  1  and the port  500 . 
         [0153]      FIG. 15  is a cross sectional view showing that the needle hub  70  is attached to the luer part  120  after the locknut  30  has been detached from the prefilled syringe  1 . The needle hub  70  has a structure in which a socket portion  71  composed of a resin material and formed to match the shape of the luer part  120  holds a needle tube  72  which is an injection needle. With the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in  FIG. 43 , the locknut obstructs the view of the user and makes it difficult to check on the positioning of the luer and the needle hub, thereby creating the danger of the user mistakenly pricking himself/herself and coming into contact with infectious material. In addition, the conventional problem that the needle hub cannot be deeply placed in and attached to the luer part due to the presence of the locknut can be fundamentally solved by Embodiment 6 since the user can readily detach the locknut  30  from the prefilled syringe  1  by handling the arms  31  and  32  in a simple fashion. 
       Other Embodiments 
       [0154]    Note that Embodiment 6 has a structure in which one projection  310  or  320  having a triangular cross section is formed on the end of each arm  31  and  32  and fitted with the convex portions  101  and  102  and concave portion  103  of the syringe body  10 . However, the following embodiments are also within the scope of the present invention. 
       7. Embodiment 7 
       [0155]    As to Embodiment 7 shown in  FIG. 16 , although the structure of the locknut  30  is substantially similar to that of Embodiment 1, the syringe body  10  has a slightly different structure. Embodiment 7 is characterized by a male screw portion  104  formed with a helical convex portion provided on the outer surface of the syringe body  10 . 
         [0156]    With using the syringe body  10  having the male screw portion  104  also, the present invention is able to achieve an equivalent effect to that of Embodiment 6. In addition, Embodiment 7 allows for a slight adjustment of the positional relationship between the syringe body  10  and the locknut  30  by changing the degree of screwing of the male screw portion  104  into the locknut  30  (i.e. how far the male screw portion  104  is screwed into the locknut  30 ). Consequently, Embodiment 7 achieves a good connection of the syringe  1  to a fixed connection port corresponding to the luer part  120  shorter than a conventional one. 
       8. Embodiment 8 
       [0157]    As to Embodiment 8 shown in  FIG. 17 , although the structure of the locknut  30  is substantially similar to that of Embodiment 6, the syringe body  10  has a slightly different structure. Embodiment 8 is configured to have a concave portion  105  which is formed by concaving the outer surface of the syringe body  10 . 
         [0158]    With using the syringe body  10  having the concave portion  105  also, Embodiment 8 is able to achieve an equivalent effect to that of Embodiment 6. In addition, since the syringe body  10  of Embodiment 8 has a smooth surface without the convex portions  101  and  102 , a problem such as the convex portions  101  and  102  of the syringe body  10  catching the user&#39;s clothes while in use can be avoided. It is a matter of course that the syringe body  10  according to Embodiment 8 must have enough thickness for the formation of the concave portion  105 . 
       9. Embodiment 9 
       [0159]    As to Embodiment 9 shown in  FIG. 18 , although the structure of the syringe body  10  is substantially similar to that of Embodiment 6, a locknut  35  has a slightly different structure. Embodiment 9 is characterized by projection sets  351  and  352 , each of which includes multiple projections, formed on the inner sides of the tip ends of arms  36  and  37 , respectively. Here, in the respective sets  351  and  352 , the projections are provided with a predetermined distance therebetween. 
         [0160]    With using the syringe body  10  having the locknut  35  also, Embodiment 9 is able to achieve an equivalent effect to that of Embodiment 6. Especially since the multiple projections of the sets  351  and  352  are fitted with the syringe body  10 , Embodiment 9 allows for a more reliable fixation of the syringe  1  and locknut  35 . 
       Additional Particulars Regarding Embodiments 6 Through 9 
       [0161]    Although the prefilled syringe  1  of the present invention has been explained with an example in which the needle hub  60  is attached after the locknut  30  being detached, the present invention is not limited to that case. Instead of a needle hub, a tubelike luer or a tube may be used. It is effective to attach, from the top, a cap or the like to the prefilled syringe  1  with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking. As such a cap, one similar to a cap for a vial container can be used. 
         [0162]    Each embodiment described above discloses a structural example of a locknut having a female screw formed therein. However, the present invention is not confined to this structure, and the prefilled syringe  1  may be appropriately connected to the port of a line system using a discontinuous thread, a cup joint, or another structure. 
         [0163]    In addition, although each embodiment above describes a structural example of a locknut having two arms, the present invention is not limited to the number of arms. Further more, instead of the arms, a tubular extension may be formed by extending the cylindrical body of the locknut in the axial direction, and projections may be provided on the inner side of the extension. In this case, it is desirable that the locknut and syringe be engaged with each other by not fitting engagement, but screwing engagement in view of the elastic deformation properties of the locknut. 
         [0164]    The luer part of the syringe used in the present invention does not necessarily have a circular cross section, and may have a rectangular, elliptic or triangle cross section, for example. Note however that, in this case, a port and a needle hub matching the shape of the luer part have to be employed. 
         [0165]    In addition, the present invention may have a structure in which multiple arms are provided that extend from the outer circumference of the top face portion positioned at the base of the luer part, and are engaged with the convex portion formed on the outer surface of the locknut. In this case, the structure is designed so that each arm is detached from the locknut by applying external forces to the syringe body in a direction different from the axial direction. 
       10. Embodiment 10 
     10-1. Overall Structure of Prefilled Syringe 
       [0166]      FIG. 19  is a cross sectional diagram showing structures of a prefilled syringe and a connector (locknut) according to Embodiment 10. For convenience of explanation, the plunger  40  is shown here in normal lateral view rather than in cross section. 
         [0167]    The prefilled syringe  1  shown in  FIG. 19  may comprise the syringe body  10 , the plunger (also referred to as a piston)  40  and the like. 
         [0168]    The syringe body  10  may be a tubular body formed by injection molding a material with high chemical resistance, such as polyethylene, polypropylene, polycarbonate or polyvinyl chloride. The tip end of the syringe body  10  is sealed by the top face portion  110 , and the luer part  120  juts out from the center of the top face portion  110 . 
         [0169]    On the other hand, the opening  12  is formed at the posterior end of the syringe body  10 . Although the luer part  120  is formed by drawing to basically give a tapered shape, the stepped portion  123  is provided in a part of the tapered shape, which thereby forms the luer base portion  121  having a smaller diameter and the luer tip portion  122  located on the tip side of the luer part  120  and having a larger diameter. A fixture  20 , to be hereinafter described, is fitted to the stepped portion  123 . In addition, the luer tip portion  122  is formed in a tapered shape in compliance with ISO6/100 so that the regular needle hub  20  can be attached thereto easily. In  FIG. 19 , the cap  15  is attached to the tip of the luer part  120 . 
         [0170]    In the following description, the longitudinal direction of the syringe body  10  is referred to as an “axial direction” while a direction perpendicular to the axial direction is referred to as a “radial direction”. 
         [0171]    The plunger  40  is made of a resin material with high chemical resistance, similarly to the syringe body  10 , and includes the plunger body  42  having a cruciform cross sectional shape for the purpose of reinforcement, at each end of which are formed disk-shaped end pieces having main surfaces in the radial direction. One of the end pieces is the pressing end portion  41  to be pressed by the user with a thumb, and the other end piece is the head portion  43  that is inserted inside the syringe body  10  in the axial direction. 
         [0172]    The packing  44  is provided at the tip of the head portion  43  in a manner to make tight contact with the internal wall of the syringe body  10 . Here, medication  100  is held in the syringe body  10 , which is internally sealed by the packing  44  and the cap  20 . 
         [0173]    When using the prefilled syringe  1  having such a structure, the user removes the cap  20  to enable discharge of the medication  100 . As the user pushes the pressing end portion of the plunger  40  into the syringe body  10  with a thumb, the medication  100  is discharged from the tip of the luer part  120  according to the depressed amount of the plunger. 
       10-2. Structures of Fixture and Locknut 
       [0174]    The prefilled syringe  1  of Embodiment 10 is constructed such that the locknut  30 , which is a connector easily detachable from the syringe body  10 , is inserted onto the luer part  120  in the axial direction and attached thereto so as to be engaged with the fixture  20  positioned at the stepped portion  123 . The locknut  30  is used in the medical field as a connection implement for connecting the prefilled syringe  10  to a fixed connection port of a transfusion line system or blood collection line system. Note that, here, the prefilled syringe  1  is adopted as a syringe for engaging with the locknut  30 ; however, the present invention may be applied to syringes other than prefilled syringes. 
         [0175]    The fixture  20  is formed by injection molding a resin material with mechanical strength and appropriate elasticity. As shown in the assembly drawing of  FIG. 20 , the fixture  20  comprises: a platy fixture body  201  having an insertion hole  202 ; two platy arms  205  and  206  extending in one direction from the periphery of the fixture body  201 ; and two platy levers  203  and  204  also extending in the opposite direction from the periphery of the fixture body  201 . 
         [0176]    The diameter of the insertion hole  202  of the fixture body  201  is slightly smaller than that of the luer tip portion  122  of the luer part  120 , but larger than that of the luer base portion  121 . The fixture  20  is inserted onto the luer part  120  through the insertion hole  202  and then forcedly shifted to fit at the luer base portion, and whereby the stepped portion  123  abuts on the periphery of the insertion hole  202  and the fixture  20  is held so as to be not easily separated from the luer part  120 . In order to favorably hold the fixture body  201  by “forced fit” at the stepped portion  123  using the insertion hole  202 , it is desirable to make the insertion hole  202  have the minimum possible diameter that enables the luer base portion  121  to pass therethrough. In addition, the diameter enabling the “forced fit” varies according to the elasticity of the material of the fixture body  201 , and therefore it is desirable to take into account the size of the luer base portion  121  and the material properties of the fixture  20  for designing the insertion hole  202 . 
         [0177]    The two arms  205  and  206  extend in the syringe axial direction, and projections  2050  and  2060 , each having a triangular cross section, are formed inside the tip ends of the arms  205  and  206 . Note that the cross-sectional shape of the projections  2050  and  2060  may be rectangular, semicircular, or other forms. 
         [0178]    The two levers  203  and  204  and the arms  205  and  206  are formed swayable so that each of these sets warps away from the syringe axis, with portions thereof adjacent to the fixture body  201  being fixed points and their tip ends spreading like open tweezers. As shown in  FIG. 20 , the levers  203  and  204  are formed to be symmetric with the two arms  205  and  206 , respectively, around the fixed points of the fixture  201 , and thereby when the levers  203  and  204  are pressed, the arms  205  and  206  open up, warping away from the syringe axis. This mechanism is for detaching the locknut  30 . Note that it is desirable to use a material having appropriate elasticity (polypropylene, for example) for the fixture  20  in order to favorably design the insertion hole  202  and achieve the swayable mechanism. 
         [0179]    The locknut  30  has a cylindrical shape having a bottom, and is formed by injection molding a resin material with high mechanical strength. A screw thread is cut on the internal surface of the lateral side portion (outer surface)  301 , which corresponds to the cylindrical part of the locknut  30 , to thereby form the female screw  3010  in compliance with, for example, ISO594-2. The female screw  3010  engages with the male screw to be hereinafter described. 
         [0180]    An insertion hole  305  is provided on the main surface portion  302  that is the bottom of the locknut  30 . The insertion hole  305  is formed to have a diameter at least larger than that of the luer tip portion  122  so that the entire luer part  120  of the prefilled syringe  1  is inserted thereto with clearance therebetween. Concave portions  303  and  304  are formed on the lateral side portion  301  of the locknut. These concave portions  303  and  304  have, for example, a rectangular cross section, and their locations and sizes are determined so that the concave portions  303  and  304  can engage with the projections  2050  and  2060  provided on the arms  205  and  206  of the fixture  20 . 
       10-3. Engagement of Syringe and Locknut 
       [0181]    As a characteristic of Embodiment 10, the engagement of the syringe body  10  and locknut  30  using the fixture  20  is described with reference to the assembly drawing of  FIG. 20 . Note that  FIG. 20  shows an operation of attaching the fixture  20  to the luer part  120 , and this operation takes place only when the fixture  20  is attached to the syringe body  10  for the first time. Once the luer part  120  and fixture  20  are attached to each other, the present invention does not require to detach them again. 
         [0182]    As to the locknut  30  having the above structure and the fixture  20  fitted with the luer base portion  121  of the luer part  120  and held at the stepped portion  123 , the user first presses the levers  203  and  204  by gripping them with fingers so as to open the tip ends of the arms  205  and  206  away from the axial direction, as shown in  FIG. 22 . While this state is maintained, the user inserts, into the insertion hole  305  along the axial direction, the luer tip portion  122  of the luer part  120  to which the fixture  20  is attached. At this point, since the insertion hole  305  has a sufficiently large diameter as compared to the luer tip portion  122  of the luer part  120 , the user can smoothly insert the luer part  120  into the locknut  30 . Note that the size of the insertion hole  305  may be set so that the insertion hole  305  is slidable over the luer tip portion  122  to some degree, and then a device preventing the locknut  30  from easily disengaging from the luer tip portion  122  may be provided. 
         [0183]    After shifting the locknut  30  sufficiently to the luer part  120  side, as the second step, the user checks on the relative positions of the concave portions  303  and  304  provided on the locknut&#39;s lateral side portion  301  and the projections  2050  and  2060  of the fixture  20 , and releases the pressure applied on the levers  203  and  204 . Herewith, the projections  2050  and  2060  of the arms  205  and  206  engage with the concave portions  303  and  304  of the locknut  30 , and whereby the locknut  30  is favorably held on the syringe body  10  by means of the fixture  20 . 
         [0184]    On the other hand, the fixture  20  and locknut  30  can, after being engaged with each other, be again detached by performing a predetermined operation (i.e. applying an external force on the fixture  20  in a direction different from the syringe axial direction) in the following manner. That is, when the user presses the levers  203  and  204  while grasping the fixture  20 , the projections  2050  and  2060  of the arms  205  and  206  are released from the concave portions  303  and  304  of the locknut  30  according to so-called “the principle of leverage”, and in this state of things, the user can pull the locknut  30  out along the axial direction. This operation can be performed in a reversible and simple fashion (for example, in one hand), and the user is therefore able to easily attach the locknut  30  to the prefilled syringe  1  when required, and detach the locknut  30 , when not required, to thereby use the prefilled syringe  1  alone. 
         [0185]      FIG. 21  is a cross sectional view showing that the prefilled syringe  1  may be connected, using the locknut  30 , to the fixed connection port  50  of a transfusion line system. The male screw of the port  50  is screwed into the female screw  3010  of the locknut  30  shown in  FIG. 21 , and herewith the luer tip portion  122  of the luer part  120  of the prefilled syringe  1  is in close contact with the packing  52  provided inside the port  50  and is inserted into the transfusion line. The locknut  30  is tightly engaged with the syringe  1  by the projections  2050  and  2060  of the arms  205  and  206  and the concave portions  303  and  304  of the locknut  30  so that the prefilled syringe  1  does not come apart from the port  50  along the axial direction even if some degree of tension is applied to the prefilled syringe  1 . As a result, the user is able to leave the prefilled syringe  1  connected to the port  50  over a long period of time and deliver a required amount of medication  100  to the inside of the port  50  by safely pushing the plunger  40  into the syringe body  10 . 
         [0186]    On the other hand,  FIG. 23  is a cross sectional view showing that the prefilled syringe  1  is connected to the direct connection port  500  of a transfusion line system after the locknut  30  has been detached from the prefilled syringe  1 . With the prefilled syringe  1  from which the locknut  30  has been detached, no obstacle exists around the luer tip portion. It is therefore possible to, without the interference of the locknut  30 , achieve a suitable connection between the prefilled syringe  1  and the port  500  by properly and tightly holding the luer tip portion  122  with the packing  52  in the port  500 . As a result, with the direct connection port  500  also, the user is able to leave the prefilled syringe  1  connected to the port  500  over a long period of time and deliver a required amount of medication  100  to the inside of the port  50  by safely pushing the plunger  40  into the syringe body  10 . 
         [0187]      FIG. 24  is a cross sectional view showing that the needle hub  60  is attached to the luer tip portion  122  after the locknut  30  has been detached from the prefilled syringe  1 . The needle hub  60  has a structure in which the socket portion  61  composed of a resin material and formed to match the shape of the luer tip portion  122  holds the needle tube  62  which is an injection needle. With the conventional prefilled syringe in which the locknut is fixed and cannot be detached therefrom as shown in  FIG. 43 , the locknut obstructs the view of the user and makes it difficult to visually determine the positioning of the luer and the needle hub, thereby creating the danger of the user mistakenly pricking himself/herself and coming into contact with infectious material. However, Embodiment 1 solves such a conventional problem since allowing for easy observation of the positional relationship around the luer between the levers  205  and  206  which spread like open tweezers from the fixture  20 . 
       Other Embodiments 
       [0188]    Note that although in Embodiment 10 the locknut  30  is attached to the syringe using the arms  205  and  206  and concave portions  303  and  304 , the following embodiments are also within the scope of the present invention. 
       11. Embodiment 11 
       [0189]    In a structural example of Embodiment 11 shown in  FIG. 25 , slit-shaped concave portions  303 E and  304 E are formed on a lateral side portion  301 E of a locknut  30 E along the circumference thereof. On the other hand, in addition to levers  203 A and  204 A similar to the levers  203  and  204  of Embodiment 10, arms  205 A and  206 A are provided, each shaped like an arc of a semicircle in cross section. These arms  205 A and  206 A extend from a fixture body  20 A, and a slit  207 A is created on the arms  205 A and  206 A adjacent to the boundary between the arms  205 A and  206 A and the fixture body  201 A. With the slit  207 A, the arms  205 A and  206 A spread like open tweezers when the user presses the levers  203 A and  204 A. On the inner side of the tip ends of the arms  205 A and  206 A, projections  2050 A and  2060 A are formed to match the shape of the slit-shaped concave portions  303 E and  304 E. 
         [0190]    Embodiment 11 with the fixture  20  and locknut  30  having such structures can achieve an equivalent effect to that of Embodiment 10. In addition, Embodiment 11 has a structure in which the arms  205 A and  206 A hold the locknut  30 E in a manner to encase it, enabling more reliably attachment of the locknut  30 E to the syringe  1  without any play. Furthermore, according to Embodiment 11, even if torque is applied to the locknut  30 E in the radial direction while in use, the engagement of the slit-shaped concave portions  303 E and  304 E and the projections  2050 A and  2060 A favorably prevents the locknut  30 A from rotating, which results in maintaining stable engagement of the syringe  1  and locknut  30 E. 
       12. Embodiment 12 
       [0191]    In a structural example of Embodiment 12 shown in  FIG. 26 , a female screw portion  303 B is spirally formed on a lateral side portion  301 B of the locknut  30 B along the circumference thereof. On the other hand, in addition to levers  203 B and  204 B similar to the levers  203  and  204  of Embodiment 10, arms  205 B and  206 B having male screw portions  2050 B and  2060 B made up of multiple projections are provided. The female screw portion  303 B and male screw portions  2050 B and  2060 B are formed so that they can be screwed with each other. The arms  205 B and  206 B are provided so as to extend from a fixture body  201 B, and spread like open tweezers when the user presses levers  203 B and  204 B. To attach a fixture  20 B to the locknut  30 B, the user spreads the male screw portions  2050 B and  2060 B by pressing the levers  203 B and  204 B, and brings the male screw portions  2050 B and  2060 B into contact with the female screw portion  303 B provided on the external peripheral surface of the locknut  30 B. Subsequently, the male screw portions  2050 B and  2060 B and the female screw portion  303 B are screwed with each other by causing relative rotation between the fixture  20 B and locknut  30 B. 
         [0192]    Embodiment 12 with the fixture  20 B and locknut  30 B having such structures can achieve an equivalent effect to that of Embodiment 10. In addition, according to Embodiment 12, it is possible to securely attach the locknut  30 B to the syringe  1  while preventing play and unwanted rotation between the fixture  20 B and locknut  30 B by adjusting the degree of screwing of the male screw portions  2050 B and  2060 B into the female screw portion  303 B (i.e. how tightly they are locked together). As a result, even if unwanted torque is applied to the locknut  30 B in the radial direction while in use, the engagement of the screw portions favorably prevents the locknut  30 B from rotating, which results in maintaining stable engagement of the syringe  1  and locknut  30 B. 
       Additional Particulars Regarding Embodiments 10 Through 12 
       [0193]    Although the prefilled syringe  1  of the above embodiments has been explained with an example in which the needle hub  60  is attached after the locknut  30  being detached, the present invention is not limited to that case. Instead of a needle hub, a tubelike luer or a tube may be used. It is effective to attach, from the top, a cap or the like to the prefilled syringe  1  with a needle hub attached thereto so as to protectively cover the needle hub and needle tube for the purpose of avoiding accidental pricking. As such a cap, one similar to a cap for a vial container can be used. 
         [0194]    The luer part of the syringe used in the present invention does not necessarily have a circular cross section, and either one of the luer tip portion and the luer base portion or both have rectangular, elliptic, or triangle cross sections. In brief, the luer tip portion must have a larger diameter than the luer base portion. 
       13. Embodiment 13 
     13-1. Structure of Connecter  1 J 
       [0195]    The following describes a structure of a connecter  1 J which is a connector of Embodiment 13, with reference to  FIG. 27 . 
         [0196]    The connector  1 J is used to fixedly hold a syringe  5 J, to be hereinafter described, on a port  61 J (see  FIG. 29 ). As shown in  FIG. 27A , the connector  1 J is made up of: a connector body  10 J as the main body thereof; and a locknut  20 J functioning as a constraint portion which constrains the shape of the connector body  10 J.  FIG. 27A  shows that, in the connecter  1 J, the connector body  10 J is free from the construction of the locknut  20 J. 
         [0197]    Of the components of the connector  1 J, the connector body  10 J is substantially tubular with a bottom, and includes a port connecting portion  11 J and a syringe connecting portion  12 J which are integrally formed. The port connecting portion  11 J is located on the opening side of the substantially tubular connector body  10 J, and a male screw  11   a  for connecting with an instrument is formed on the internal surface of the tubular body. In addition, knurling with straight ridges and grooves is provided on the outer surface of the tubular body so as to prevent slippage in an operation of connecting the connector  1 J to an instrument. 
         [0198]    The syringe connecting portion  12 J is positioned, within the connector body  10 J, at the bottom face thereof and part of the lateral wall adjacent to the bottom face. The bottom-face part of the syringe connecting portion  12 J is divided by a slit  13 J into two, up and down halves—an upper bottom member  121 J and a lower bottom member  122 J—in the y direction in the figure. The halved bottom members  121 J and  122 J are structured so that the slit  13 J therebetween is opened and closed according to the constraint force exerted by the locknut  20 J onto the connector body  10 J. A single female screw  12   a  discontinued by the slit  13 J is formed on the outer surface of the syringe connecting portion  12 J. 
         [0199]    As shown in  FIG. 27B , the upper and lower bottom members  121 J and  122 J divided by the slit  13 J into up and down halves in the y direction respectively have a petal-like shape, and swing in the y direction in the figure when no constraint force is exerted by the locknut  20 J. Formed on the respective bottom members  121 J and  122 J are semicircular cutouts  121   h  and  122   h . The chords of the cutouts  121   h  and  122   h  correspond to the lines extending from the edges of the bottom members  121 J and  122 J exposed to the slit  13 J. In the state shown in  FIG. 27B , the cutouts  121   h  and  122   h  oppose each other across a space, forming an oval shape. Here, a hypothetical inscribed circle  12   h  of the cutouts  121   h  and  122   h  has a diameter of φD 0 . 
         [0200]    Referring back to  FIG. 27A , the locknut  20 J is placed to encircle the periphery of the syringe connecting portion  12 J in the connector body  10 J, and a male screw  21 J is provided on the internal peripheral surface as shown in the closeup in the figure. The male screw  21 J is to be screwed with the female screw  12   a  formed on the outer surface of the syringe connecting portion  12 J in the connector body  10 J. In addition, on the outer peripheral surface of the locknut  20 J, knurling, similar to the one provided on the outer surface of the port connecting portion  11 , is performed on the outer peripheral surface of the locknut  20 J to thereby prevent slippage. When the locknut  20 J is positioned, in the x direction, to the right of the syringe connecting portion  12 J as shown in  FIG. 27 , the syringe connecting portion  12 J spreads like open tweezers toward the bottom side. Herewith, the cutouts  121   h  and  122   h  form an oval shape as described above. 
       13-2. State-Changeable Mechanism of Connector  1 J 
       [0201]    The following describes a state-changeable mechanism of the connector  1 J having the above-mentioned structure. 
         [0202]    In  FIG. 27A , the locknut  20 J is located, in the x direction, on the rightmost side of the syringe connecting portion  12 J in the connector body  10 J. In this configuration, the locknut  20 J does not apply constraint force to the syringe connecting portion  12 J. 
         [0203]    When the locknut  20 J in the configuration shown in  FIG. 27A  is shifted, in the x direction, to the left of the syringe connecting portion  12 J as being screwed into the female screw  12   a , the syringe connecting portion  12 J becomes subject to constraint force exerted by the locknut  20 J in the direction that the slit  13 J becomes narrowed—i.e. in the direction that the space between the petal shaped bottom members  121 J and  122 J becomes narrowed. When the locknut  20 J has been shifted to the vicinity of the bottom, the shape of the syringe connecting portion  12 J that previously spread like open tweezers has been transformed to be substantially tubular. With the transformation, the space between the cutouts  121   h  and  122   h  narrows, and the diameter of the inscribed circle  12   h  is also reduced to less than the diameter φD 0 . 
         [0204]    It is preferable that the connector body  10 J be made of a material having elastic properties (e.g. a resin material) in consideration for repetitive attachment and detachment. Although the syringe connecting portion  12 J changes its shape under the constraint force of the locknut  20 J, the transformation is performed within the elastic range of the material constituting the connector body  10 J. Accordingly, the syringe connection portion  12 J returns to the state shown in  FIGS. 27A and 27B  without any deformation once the constraint force of the locknut  20 J is removed. 
         [0205]    Thus, the connector  1 J has a mechanism that the space between the cutouts  121   h  and  122   h  on the bottom members  121 J and  122 J widens and narrows simply by tightening and loosening the locknut  20 J. This mechanism is reversible and can be operated repeatedly. 
         [0206]    The general structure of a syringe  5 J is described with reference to  FIG. 28 . 
         [0207]    The syringe  5 J, part of which is shown in  FIG. 28A , is a prefilled syringe, and a luer part  51 J juts or extends out at the right-hand end of a syringe body  52 J. Formed on the base side of the luer part  51 J is a neck portion  53 J having a reduced diameter. Although no illustration is given, the syringe  5 J includes a plunger, a packing and the like, and the tubular part of the syringe body  52 J is filled with the liquid medication. 
         [0208]    Among the components of the syringe  5 J, the luer part  51 J has a tapered shape and a maximum outer diameter of φD 1 . The outer diameter φD 1  is smaller than the diameter D 0  of the inscribed circle  12   h  of the connector  1 J in the open state shown in  FIG. 27 , i.e. (φD 1 &lt;φD 0 ). The neck portion  53 J on the base side of the luer part  51 J is tubular with a diameter smaller than the diameter φD 1 . 
         [0209]    A step is made in a part of the luer part  51 J close to the neck portion  53 J so as to form an engaging portion  51   a.    
         [0210]    The connection of the above-mentioned syringe  5 J and connector  1 J are described next also with reference to  FIG. 28 . 
         [0211]    As shown in  FIG. 28A , the locknut  20 J of the connector  1 J is set back, within the syringe connecting portion  12 J, to the side closest to the port connecting portion  11 J, and whereby the connector body  10 J is kept free from the constraint force of the locknut  20 J in the radial direction, similar to the case of  FIG. 27 . The luer part  51 J of the syringe  5 J is inserted toward the inscribed circle  12   h  (not shown in  FIG. 28 ) of the cutouts  121   h  and  122   h  of the connector  1 J in this state (arrow B). Here, the maximum outer diameter D 1  of the luer part  51 J and the diameter φD 0  of the inscribed circle  12   h  satisfy φD 1 &lt;φD 0 , which thereby allows for smooth insertion of the luer part  51 J. 
         [0212]    The insertion of the luer part  51 J into the connector  1 J is done when the neck portion  53 J reaches an inner bottom surface  123 J of the connector  1 J. While the center of the syringe  5 J in the radial direction is substantially aligned with that of the connector  1 J, the locknut  20 J of the connector  1 J is rotated along the female screw  12   a  and shifted to the left in the figure. The shifting is done when the locknut  20 J substantially reaches the left end of the connector body  10 J. 
         [0213]    The female screw  12   a  on the outer surface of the syringe connection portion  12 J is formed up to the bottom members  121 J and  122 J (see  FIG. 1 ) so that the locknut  20 J stops thereat. 
         [0214]    As shown in  FIG. 28B , in a condition where the locknut  20 J has been shifted to the leftmost side of the syringe connection portion  12 J, the syringe connection portion  12 J that previously spread like open tweezers as in  FIG. 28A  closes under the constraint force exerted by the locknut  20 J to be substantially tubular. With the transformation, the space between the cutouts  121   h  and  122   h  narrows, and the diameter of the inscribed circle  12   h  is also reduced. Then, the inscribed circle  12   h  formed by the cutouts  121   h  and  122   h  becomes substantially circular in the state of  FIG. 28B . At this point, the diameter of the inscribed circle  12   h  of the connector  1  is φD 2 . The relationship between the diameters φD 1  and φD 2  is φD 2 &lt;φD 1 . Namely, in the state of  FIG. 28B , the inner bottom surface  123 J of the connector  1 J is engaged with the engaging portion  51   a  of the syringe  5 J, and the syringe  5 J is fixedly held by the connector  1 J. 
         [0215]    Note that, in  FIG. 28B , the diameter φD 2  of the open hole formed by the cutouts  121   h  and  122   h  in the connector  1 J is slightly larger than the outer diameter of the neck portion  53 J of the syringe  5 J so as to have a clearance therebetween. However, this clearance is not necessarily provided. 
         [0216]    As has been described, the connector  1 J is structured to be freely attachable to and detachable from the syringe  5 J by simply handling the locknut  20 J. Here, the connector  1 J may be provided to the user as an accessory of the syringe  5 J, or separately by itself. 
         [0217]    In order to change a state of the syringe  5 J from one in which the connector  1 J is attached, as shown in  FIG. 28B , to one in which the connector  1 J is detached, as shown in  FIG. 28A , a reverse process of the above-mentioned procedure for connecting the connector  1 J may be performed. 
         [0218]    Referring to  FIG. 29 , the following describes a method of connecting the syringe  5 J, to which the connector  1 J is attached, to a port of a medical instrument in the luer-lock style. In  FIG. 29 , an extension tube  6 J with a port attached thereto is used as an example of a connection target to which the syringe  5 J is connected in the luer-lock style. 
         [0219]    The extension tube  6 J of the connection target includes the port  61 J provided at one end of a tube  62 J, as shown in  FIG. 29 . Within the port  61 J, a female screw  61   a  is formed on the outer surface of the tubular body. The female screw  61   a  corresponds to the male screw  11   a  (not shown in  FIG. 29 ; refer to  FIGS. 27 and 28 ) of the connector  1 J (i.e. the male screw  11   a  can be screwed into the female screw  61   a ). 
         [0220]    On the end face of the port  61 J, a hole  63 J is provided in the central region. This hole  63 J is connected to the inner duct of the tube  62 J. The inner diameter of the hole  63 J is set slightly smaller than the maximum outer diameter φD 1  of the luer part  51 J of the syringe  5 J, and a portion of the luer part  51 J of the syringe  5 J can enter the inner duct through the hole  63 J when the syringe  5 J is connected to the extension tube  6 J. 
         [0221]    For connecting the syringe  5 J and the extension tube  6 J to each other, the user brings the connector  1 J attached to the proximity of the luer part  51 J of the syringe  5 J (see  FIG. 28 ) forward (arrow E) with respect to the extension tube  6 J, and when the connector  1 J and the port  61  of the extension tube  6 J make contacts, the user starts rotating the connector  1 J in the direction of arrow C. Herewith, the male screw  11   a  provided in the connector body  10 J (see  FIGS. 27 and 28 ) is progressively screwed into the female screw  61   a  on the port  61 J of the extension tube  6 J. At this point, the luer part  51 J of the syringe  5 J is being inserted into the hole  63 J of the extension tube  6 J. The male screw  11   a  is continuously screwed into the female screw  61   a  until the space between the external peripheral surface of the luer part  51 J and the periphery of the hole  63 J is closed. 
         [0222]    In the above manner, the luer-lock connection of the syringe  5 J and extension tube  6 J is completed. Since the connection in the luer-lock style is stable, the syringe  5 J and the extension tube  6 J are less likely to come disengaged or loose from each other over a long period of time. 
         [0223]    Referring to  FIG. 30 , the following describes a method of connecting the syringe  5 J to a port of a medical instrument in the luer-slip style. In  FIG. 30 , a coinfusion port  7 J and an injection needle  8 J are used as examples of connection targets to which the syringe  5 J is connected. 
         [0224]    For the connection in the luer-slip style, the syringe  5 J to which the connector  1 J is not attached is used, as shown in  FIG. 30 . As to the syringe  5 J, the user may use one to which no connector is originally attached, or alternatively obtain one with the connector  1 J attached thereto and use this syringe after detaching the connector  1 J therefrom. The connector  1 J can be readily detached according to a reverse process of the above-mentioned procedure shown in  FIG. 28 . 
         [0225]    For the connection in the luer-slip style, the luer part  51 J of the syringe  5 J is simply inserted into a port of a connection-target medical instrument. For example, the connection of the syringe  5 J to the coinfusion port  7 J is completed simply by inserting the luer part  51 J of the syringe  5 J into a valve plug (not shown) provided in a cover body  71 J. Herewith, the interior of the syringe  5 J and the interior of the tubes  72 J and  73 J of the coinfusion port  7 J are communicated to each other. 
         [0226]    The valve plug of the coinfusion port  7 J is an elastic thin film, and a slit to receive the luer part  51 J is formed in a part of the valve plug. Since such matters are public knowledge, the descriptions are omitted here. 
         [0227]    Next, for connecting the syringe  5 J and the injection needle  8 J to each other, a needle hub  82 J of the injection needle  8 J is mounted on the luer part  51 J of the syringe  5 J. The syringe  5 J and the injection needle  8 J are connected to each other when an internal peripheral surface  82   f  of the needle hub  82 J becomes tightly attached to the external peripheral surface  51   f  of the luer part  51 J. Although no graphic representation is given, the needle tube  81 J juts out also inside the needle hub  82 J, and the jutted part is inserted into an inner hole of the luer part  51 J when the syringe  5 J and the injection needle  8 J are connected to each other. The needle hub  82 J and the inner hole of the luer part  51 J are tightly fitted to each other while the injection needle  8 J being connected to the syringe  5 J. That is, the needle hub  81 J and the inner hole are designed so that the liquid medication will not leak out therefrom or bacteria will not enter therefrom. 
         [0228]    The luer-slip connection of the syringe  5 J and another medical instrument has been described by presenting two examples above. The syringe  5 J of  FIG. 30  does not have the connector  1 J attached thereto, allowing for quick luer-slip connection. 
         [0229]    Although, there are various medical instruments that can be connected to the syringe  5 J in the luer-slip style besides the above two examples, the connection operations for those instruments are the same as above. 
         [0230]    Advantages of Connector  1 J and Syringe  5 J Having Connector  1 J Attached Thereto 
         [0231]    As has been described above and also shown in  FIG. 28 , the connector  1 J of Embodiment 13 is attachable to and detachable from the syringe  5 J by simply performing the screwing operation of the locknut  20 J. 
         [0232]    Thus, in the medical practices, the user is able to readily attach and detach the connector  1 J to/from the syringe  5 J according to need. 
         [0233]    Thus, since being able to attach and detach the connector  1 J functioning as a connector to/from the syringe  5 J if necessary, the user can use the detached connector  1 J with another syringe. This results in a reduction in the cost burden on the user and allows for an excellent operational performance of the syringe  5 . Furthermore, the syringe  5 J can be connected to the port of another medical instrument in either the luer-slip or luer-lock style. 
         [0234]    When connecting the injection needle  8 J to the syringe  5 J, the user can use the syringe  5 J from which the connector  1 J has been detached, as shown in  FIG. 30 . Thus, the syringe  5 J is also effective in preventing the user from mistakenly pricking himself/herself. 
         [0235]    Note that the connector  1 J, which functions as a connector, does not have to be provided with every syringe  5 J when supplied to the user, and may be singularly provided to the user instead. In such a case, the user may attach/detach the connector  1 J to/from the syringe  5 J according to need. Thus, the connector  1 J can be attached and detached, according to the connection style of the syringe  5 J with the port, at the stages of treatment and medical care in the medical practices. As a result, operating efficiency can be improved, and the number of syringe types required to be prepared in advance can be reduced. 
         [0236]    Additional Particulars Regarding Embodiment 13 
         [0237]    Although Embodiment 13 is described with an example in which the connector body  10 J is fitted to the extension tube  6 J by screwing the locknut  20 J into the connector body  10 J and thereby making the locknut  20 J shift toward the connector body  10 J, the present invention is not limited to the case. The same effect as that of Embodiment 13 can be achieved, for example, with a connector having, instead of the locknut  20 J, a ring body with no screw provided on the internal peripheral surface thereof. Here, the connector body  10 J is fitted to the extension tube  6 J by sliding the ring body toward the connector body  10 J. 
         [0238]    Note that, in the case of adopting such a sliding mechanism, it is required to implement a measure that prevents the ring body from shifting back to the original position when the connector body  10 J is fitted to the extension tube  6 J. Fixing the ring body with a pin is an example of such a measure. 
         [0239]    Although, in the above embodiment, the connection target is the (prefilled) syringe  5 J filled with liquid medication in advance, the above operation remains the same even if a different type of syringe, other than a prefilled syringe, is used. 
       14. Embodiment 14 
       [0240]    The structure of a connector  1 K of Embodiment 14 which functions as a connector is described with the aid of  FIG. 31 . 
         [0241]    As shown in  FIG. 31A , the connector  1 K may be made up of three components: split frames  11 K and  12 K; and a coupling portion  13 K coupling the sides of the split frames  11 K and  12 K. These three components are integrally formed. Of them, the split frames  11 K and  12 K have a shape as if created by halving, along the axis, a hollow cylinder having a bottom.  FIGS. 31A and 31B  show the state where the split frames  11 K and  12 K are open (hereinafter, “the open position”). 
         [0242]    Each of the split frames  11 K and  12 K having a shape as if created by halving a cylinder hollow having a bottom includes a semicylindrical portion  112 K/ 122 K and a semicircular bottom portion  11 K/ 121 K. Formed on the semicylindrical portions  112 K and  122 K are sets of tabs  11   m  and  12   m  to be interlocked with each other. That is, the tabs  11   m  and  12   m  function as coupling members of the split frames  11 K and  12 K, and become interlocked with each other when the split frames  11 K and  12 K are coupled. These tabs  11   m  and  12   m  are designed so that, when once they are interlocked with each other, the coupling will not be disconnected unless an operation of pulling the tabs  12   m  outward is performed. Cutouts  11   h  and  12   h  are formed on the bottom portions  111 K and  112 K that butt against each other when the split frames  11 K and  12 K are engaged using the tabs  11   m  and  12   m  (hereinafter, “the closed position”). Each of the cutouts  11   h  and  12   h  has the shape of a semicircle with a chord coinciding with the halving line of the split frames  11 K and  12 K. 
         [0243]    Furthermore, male screw portions  11   n  and  12   n  are provided on the inner surface of the semicylindrical portions  112 K and  122 K of the split frames  11 K and  12 K. These male screw portions  11   n  and  12   n  form a single, unbroken male screw when the split frames  11 K and  12 K are in the closed position. 
         [0244]    The wall thickness of the coupling portion  13 K is thinner than that of the individual split frames  11 K and  12 K, and the coupling portion  13 K will not be dismembered after repetitive opening and closing of the split frames  11 K and  12 K. 
         [0245]    The opening-and-closing mechanism of the connector  1 K having the above structure is described next with the aid of  FIG. 31B  showing the connector  1 K of  FIG. 31A  viewed from arrow A. 
         [0246]    As shown in  FIG. 31B , in an anterior view, each of the split frames  11 K and  12 K is semicircular. When folded at the coupling portion  13 , the split frames  11 K and  12 K face to each other, and the tabs  11   m  and  12   m  interlock with each other. Thus, the connector  1 K is substantially in the shape of a cylinder having a bottom when the tabs  11   m  and  12   m  engage with each other (i.e. in the closed position). 
         [0247]    Thus, when the split frames  11 K and  12 K are joined together, the cutouts  11   h  and  12   h  provided on the split frames  11 K and  12 K also face to each other to form a circular hole with a diameter of φD 1 . 
         [0248]    Note that the split frames  11 K and  12 K and the coupling portion  13 K, all of which are integrally formed, are preferably made of, for example, a resin material in order to achieve the above-mentioned functions. 
         [0249]    A general structure of a syringe  5 K is described with the aid of  FIG. 32 . 
         [0250]    The syringe  5 K, a part of which is shown in  FIG. 32 , is a prefilled syringe, and a luer part  51 K juts out at the right-hand end of a syringe body  52 K. Formed on the base side of the luer part  51 K is a neck portion  53 K having a reduced diameter. Although no illustration is given, the syringe  5 K includes a plunger, a packing and the like, and the tubular part of the syringe body  52 K is filled with the liquid medication. 
         [0251]    Among the components of the syringe  5 K, the luer part  51 K has a tapered shape and a maximum outer diameter of φD 3 . The outer diameter φD 3  is larger than the diameter φD 1  of the hole formed by the cutouts  11   h  and  12   h  in  FIG. 31  (i.e. φD 3 &gt;φD 1 ). The neck portion  53 K located on the base side of the luer part  51 K is in the shape of a cylinder with an outer diameter of φD 2 . 
         [0252]    A step is made in a part of the luer part  51 K close to the neck portion  53 K so as to form an engaging portion  51   n.    
         [0253]    The connection of the above-mentioned syringe  5 K and connector  1 K is described next with reference to  FIGS. 31 and 32 . 
         [0254]    The luer part  51 K of the syringe  5 K is inserted into the connector  1 K in the open position as shown in  FIG. 31A  and positioned in a manner that the neck portion  53 K sets in the edge of either the cutout  11   h  or  12   h . At this point, the syringe  5 K and the connector  1 K are maintained so that their axes substantially coincide with each other. 
         [0255]    Next, while the syringe  5 K is held not to move with respect to the connector  1 K, the split frames  11 K and  12 K are folded at the coupling portion  13 K so that the openings of the split frames  11 K and  12 K face to each other. The connector  1 K has the shape of a cylinder having a bottom when the tabs  11   m  and  12   m  of the split frames  11 K and  12 K interlock with each other. At this point, the cutouts  11   h  and  12   h  form a circular hole with an inner diameter of φD 1 . 
         [0256]    The syringe  5 K is thus engaged, at the neck portion  53 K, with the connector  1 K in the closed position. That is, the maximum outer diameter φD 3  of the luer part  51 K is larger than the inner diameter φD 1  of the hole formed by the cutouts  11   h  and  12   h , and the engaging portion  51   n  of the luer part  51 K is fixedly held by inner bottom faces  111   n  and  121   n  of the connector  1 K. Thus, the syringe  5 K and the connector  1 K are connected to each other. The tabs  11   m / 12   m  of each set are provided at two locations on the split frame  11 K/ 12 K, and when these tabs  11   m  and  12   m  once interlock with each other, the connector  1 K does not return to the open position unless the disengagement operation (releasing the coupling of the tabs  11   m  and  12   m ) is conducted. 
         [0257]    Note that the male screw portions  11   n  and  12   n , each provided on the split frame  11 K/ 12 K of the connector  1 K, are designed to form one unbroken male screw across a line of junction  1 KL of the split frames  11 K and  12 K. 
         [0258]    Referring to  FIG. 32 , the following describes a method of connecting the syringe  5 K, to which the connector  1 K is attached, to a port of another medical instrument in the luer-lock style. In  FIG. 32 , an extension tube  6 K with a port attached thereto is used as an example of a connection target to which the syringe  5 K is connected. 
         [0259]    The extension tube  6 K being a connection target includes a port  61 K provided at one end of a tube  62 K, as shown in  FIG. 32 . Within the port  61 K, a female screw portion  61   n  is formed on the outer surface of the tubular body. The female screw portion  61   n  corresponds to the male screw portions  11   n  and  12   n  of the connector  1 K. Although no illustration is given, a hole is provided in the central region of the end face of the port  61 K, and functions as an opening of the inner duct of the tube  62 K. 
         [0260]    The hole in the central region of the port  61 K has an inner diameter slightly smaller than the maximum outer diameter φD 3  of the luer part  51 K of the syringe  5 K. Thus, the hole of the port  61 K is designed so that the luer part  51 K of the syringe  5 K can be inserted thereinto. 
         [0261]    For connecting the syringe  5 K and the extension tube  6 K to each other, the user brings the connector  1 K attached to the syringe  5 K forward (arrow B) with respect to the port  61 K of the extension tube  6 K. When the connector  1 K and the port  61 K of the extension tube  6 K make contacts, the user starts rotating the connector  1 K in the direction of arrow C and still brings the connector  1 K forward. Herewith, the male screw portions  11   n  and  12   n  provided in the split frames  11 K and  12 K are progressively screwed into the female screw portion  61   n  on the port  61 K of the extension tube  6 K. In parallel with the screwing operation, the luer part  51 K of the syringe  5 K is gradually inserted into the hole on the end face of the port  61 K of the extension tube  6 K. Subsequently, when the male screw portions  11   n  and  12   n  of the connector  1 K are completely screwed into the female screw portion  61   n  of the port  61 K, the syringe  5 K and the extension tube  6 K are connected to each other. 
         [0262]    Since the connection of the syringe  5 K and the extension tube  6 K with the connector  1 K therebetween (the luer-lock connection) is stable, the syringe  5 K and the extension tube  6 K are less likely to disengage or loose from each other over a long period of time. 
         [0263]    Referring to  FIG. 33 , the following describes a method of connecting the syringe  5 K and another medical instrument in the luer-slip style. In  FIG. 33 , a coinfusion port  7 K and an injection needle  8 K are used as examples of connection targets to which the syringe  5 K is connected. 
         [0264]    For the connection in the luer-slip style, the syringe  5 K to which the connector  1 K is not attached is used, as shown in  FIG. 33 . As to the syringe  5 K, the user may use a syringe to which no connector is originally attached, or alternatively obtain a syringe with the connector  1 K attached and use this after detaching the connector  1 K therefrom. The connector  1 K can be readily detached by releasing the coupling of the interlocking tabs  11   m  and  12   m.    
         [0265]    In the connection in the luer-slip style, the luer part  51 K of the syringe  5 K is simply inserted into a port of a connection-target medical instrument. For example, the connection of the syringe  5 K to the coinfusion port  7 K is completed simply by inserting the luer part  51 K of the syringe  5 K into a valve plug (not shown) provided in a cover body  71 K. Herewith, the interior of the syringe  5 K and the interior of the tubes  72 K and  73 K of the coinfusion port  7 K are communicated to each other. 
         [0266]    The valve plug of the coinfusion port  7 K is an elastic thin film, and a slit to receive the luer part  51 K is formed in a part of the valve plug. Since such matters are public knowledge, the descriptions are omitted here. 
         [0267]    Next, for connecting the syringe  5 K and the injection needle  8 K to each other, a needle hub  82 K of the injection needle  8 K is mounted on the luer part  51 K of the syringe  5 K. The syringe  5 K and the injection needle  8 K are connected to each other when an internal peripheral surface  82   f  of the needle hub  82 K becomes tightly attached to the external peripheral surface  51   f  of the luer part  51 K. Although no graphic representation is given, the needle tube  81 K juts out also inside the needle hub  82 K, and the jutted part is inserted into an inner hole of the luer part  51 K when the syringe  5 K and the injection needle  8 K are connected to each other. The needle hub  82 K and the inner hole of the luer part  51 K are tightly fitted to each other while the injection needle  8 K being connected to the syringe  5 K. That is, the needle hub  81 K and the inner hole are designed so that the liquid medication will not leak out therefrom or bacteria will not enter therefrom. 
         [0268]    The luer-slip connection of the syringe  5 K and another medical instrument has been described by presenting two examples above. The syringe  5 K of  FIG. 33  does not have the connector  1 K attached thereto, allowing for quick luer-slip connection. 
         [0269]    Although there are various medical instruments can be connected to the syringe  5 K in the luer-slip style besides the above two examples, the connection operations for those instruments are the same as above. 
         [0270]    Advantages of Connector  1 K and Syringe  5 K Having Connector  1 K Attached Thereto 
         [0271]    As has been described above and also shown in  FIG. 31 , the connector  1 K of Embodiment 14 is composed of the split frames  11 K and  12 K and the coupling portion  13 K, and allows for easy attachment to the syringe  5 K by the coupling operation of the two split frames  11 K and  12 K as well as easy detachment from the syringe  5 K by releasing the interlocking tabs  11   m  and  12   m  and opening the split frames  11 K and  12 K. On the other hand, unless the interlocking tabs  11   m  and  12   m  are released, an incident in which the split frames  11 K and  12 K open up during the use of the syringe  5 K or the like is avoided. 
         [0272]    Thus, since the user is able to attach and detach the connector  1 K to/from the syringe  5 K as the need arises, the connector  1 K has advantageous effects of (1) reducing the cost burden on the user, (2) not causing hindrance to the work performance when the syringe  5 K is used, and (3) enabling connection of the syringe  5 K to the port of another instrument in either the luer-slip or luer-lock style. The syringe  5 K having the connector  1 K attached thereto also exhibits these advantages. 
         [0273]    When connecting the injection needle  8 K to the syringe  5 K, the user can use the syringe  5 K from which the connector  1 K has been detached, as shown in  FIG. 33 . Thus, the syringe  5 K is also effective in preventing the user from mistakenly pricking himself/herself. 
         [0274]    Note that the connector  1 K does not have to be provided with every syringe  5 K when supplied to the user, and may be singularly provided to the user instead. In such a case, the user may attach/detach the connector  1 K to/from the syringe  5 K according to need. 
         [0275]    If using the syringe  5 K having the connector  1 K attached thereto for treatment and testing in the medical practices, the user is able to select whether to attach or detach the connector  1 K according to the connection style of the syringe to the port. Thus, using the syringe  5 K with the connector  1 K attached thereto achieves high efficiency in the medical practices. 
       15. Embodiment 15 
       [0276]    A connector  2  of Embodiment 15 is described with the aid of  FIG. 34 . 
         [0277]    The connector  2 K is composed of split frames  21 K and  22 K as shown in  FIG. 34 , and differs from the connector  1 K in that these split frames  21 K and  22 K are separated from each other. That is, the connector  2 K can be said to be the connector  1 K of Embodiment 14 from which the coupling portion  13 K is removed. Note however that the connector  2  has additional tabs  11   m  and  12   m  formed on the split frames  21 K and  22 K at the locations corresponding to where the coupling portion  13 K is attached. 
         [0278]    Since other components of the connector  2 K are the same as those of the connector  1 K, the descriptions are omitted here. 
         [0279]    Attachment of the connector  2 K to the syringe  5 K is achieved by setting the neck portion  53 K of the syringe  5  in the cutouts  21   h  and  22   h  while the split frames  21 K and  22 K are separated from each other, and then interlocking the tabs  11   m  of the split frame  21 K and the tabs  12   m  of the split frame  22 K. Here, the relationships of the inner diameter of the hole formed by the cutouts  21   h  and  22   h  with the maximum outer diameter of the luer part  51 K of the syringe  5 K, and with the outer diameter of the neck portion  53 K are the same as those of connector  1 K of Embodiment 14 above. 
         [0280]    The connector  2 K is easily detached from the syringe  5 K by doing the reverse of the above procedure, i.e. releasing the interlocking tabs  11   m  and  12   m . Accordingly, also when using the connector  2 K according to the present embodiment, the user is able to easily attach and detach the connector  2 K to/from the syringe  5 K as the need arises. 
         [0281]    As a result, the connector  2 K of Embodiment 15 also has advantageous effects of (1) reducing the cost burden on the user, (2) not causing hindrance to the work performance when the syringe  5 K is used, and (3) enabling connection of the syringe  5 K to the port of another instrument in either the luer-slip or luer-lock style. 
       16. Embodiment 16 
       [0282]    A connector  3 K of Embodiment 16 is described next with the aid of  FIG. 35 . 
         [0283]    The connector  3 K is characterized by the split balance of split frames  31 K and  32 K different from that of split frames  11 K and  12 K of the connector  1 K, as shown in  FIG. 35 . That is, while the split frames  11 K and  12 K of the connector  1 K have a shape as if they were formed by halving, along the axis, a hollow cylinder with a bottom, the split frame  32 K of the connector  3 K according to the present embodiment has a shape as if it was formed by halving only the bottom face and the vicinity thereof of a hollow cylinder with a bottom. 
         [0284]    The opening and closing of the connector  3 K is basically the same as that of the connector  1 K shown in  FIG. 31 . 
         [0285]    Besides the advantageous effects of the connector  1 K, the connector  3 K has an additional advantage of having a cylindrical part which exhibits higher stiffness when the connector  3 K is being screwed on another medical instrument (e.g. the extension tube  6 K of  FIG. 32 ), as compared to that of the connector  1 K. That is, when a male screw  31   n  of the connector  3 K is screwed into the female screw of the medical instrument to thereby join the connector  3 K with the medical instrument, the cylindrical part of the connector  3 K receives a force also in the outer radial direction. At this point, the connector  3 K whose cylindrical part is not split has an advantage in exhibiting higher stiffness in the radial direction than the connector  1 K whose cylindrical part is split. 
         [0286]    This means that the connector  3 K enables to set the syringe more firmly on the port of another medical instrument. 
       Additional Particulars Regarding Embodiments 14 Through 16 
       [0287]    In Embodiments 14 to 16 above, the features, functions and effects of the present invention are described by taking as examples three kinds of connectors  1 K,  2 K and  3 K, however, the present invention is not limited to those. 
         [0288]    Although, in Embodiment 14 above, a prefilled syringe filled with liquid medication in advance is used as an example of the syringe, the above-mentioned functions and effects remain the same even if a syringe of a different type is used. 
         [0289]    In Embodiments 14 to 16, the connector  1 K,  2 K or  3 K is connected to the syringe  5 K by using the neck portion  53 K formed on the base side of the luer part  51 K of the syringe  5 K. However, it is not necessary that the neck portion  53 K is formed on the base side of the luer part  51 K. For example, similar functions and effects to the above can be achieved by providing a narrowed part (which corresponds to the neck portion) on a part of the external peripheral surface of the syringe body  52 K and forming a connector to correspond to the narrowed part. 
       17. Embodiment 17 
       [0290]      FIGS. 36A ,  36 B,  36 C and  36 D illustrate a structure of a syringe of Embodiment 17. 
         [0291]    A syringe  100 L is a prefilled syringe filled with liquid medication  110 L in advance, and allows for speedy insertion and removal into/out of either the luer-lock coinfusion port or the luer-slip coinfusion port. 
         [0292]    Regarding the syringe  100 , as shown in  FIG. 36A , a cylindrical syringe portion  120 L is filled with the liquid medication  110 L and subsequently sealed by a plunger portion  150 L, and a lock part  130 L (which is an example of a connection supporting member) is freely rotatably coupled to one end of the syringe portion  120 L by means of a coupling pin  160 L (which is an example of a pin). 
         [0293]    In the syringe part  120 L, a cylindrical luer part  140 L extends from one end (hereinafter referred to as “the first end”) of a cylindrical syringe body  121 L, and a flange  121   a  is provided at the opposite end to the first end (hereinafter referred to as “the second end”). 
         [0294]    The luer part  140 L is cylindrical, and may be composed of: a 1 st  luer portion  144 L with a diameter d 1  on the base side; and a tapered 2 nd  luer portion  141 L located on the tip side of the luer part  140 L and having a tip-end diameter d 2  and a rear-end diameter d 3 . With this arrangement, d 3 &gt;d 2  and d 3 &gt;d 1 . 
         [0295]    The lock part  130 L is made of a resin material, and is a cylindrical nut with a bottom for engaging the syringe  100 L and a connection-target instrument. A through hole  134 L of a diameter d 4  is provided on the bottom face of the lock part  130 L, and through holes  132   a  and  132   b  with rectangular openings are provided on the lateral side of the cylindrical body. 
         [0296]    Note that d 4  is larger than d 3  to enable the 2 nd  luer portion  141 L to pass through the through hole  134 L. 
         [0297]    The coupling pin  160 L is a substantially U-shaped pin for engaging the lock part  130 L and the luer part  140 L, and has a function of engaging with the 1 st  luer portion  144 L while penetrating through the hull of the lock part  130 L to be thereby fitted with the lock part  130 L. 
         [0298]    To be more specific, as shown in  FIG. 36D  which is a cutaway view of the coupling pin  160 L fitted with the lock part  130 L and cut parallel to the main surface thereof, the coupling pin  160 L is a substantially U-shaped pin having two symmetric extending portions  163 L extending from a rectangular base portion  161 L. Stepped portions  162 L, which abut against the lock part  130 L when inserted thereinto, are provided at the base of the extending portions  163 L, and a projecting portion  163   a  is provided on the outer side of each extending portion  163 L, towards the tip end thereof. 
         [0299]    Provided in the center of the groove  164 L formed between these two extending portions  163 L is a concave portion  165 L to which the 1st luer portion  144 L is fitted. 
         [0300]    There is no problem whether the lock part  130 L and coupling pin  160 L are detached or attached from/to the syringe  100 L when the syringe  100 L is delivered to a medical practice site. Here, for convenience of explanation, the syringe  100 L is used from which the lock part  130 L and coupling pin  160 L have been detached at the time of delivery. 
         [0301]    The following explains how to use the syringe  100 L. 
         [0302]    Connection with Luer-Lock Coinfusion Port 
         [0303]    When a coinfusion port to which the syringe  100 L is to be connected is a luer-lock coinfusion port, a person (hereinafter, the “operator”) inserts the luer part  140 L into the through hole  134 L of the lock part  130 L, as shown in  FIG. 36A . Subsequently, the operator inserts the coupling pin  160 L into the through holes  132   a  and  132   b  of the lock part  130 L as shown in  FIG. 36B , and pushes the coupling pin  160 L thereinto until the edges of the stepped portions  162 L of the lock part  130 L make contacts with edges  162   a  of both sides of the through hole  132   a , as shown in  FIGS. 37A to 37F . 
         [0304]    At this point, the projecting portions  163   a  of the coupling pin  160 L go over contact points  162   b  on both sides of the through hole  132   b  and thereby prohibit the coupling pins  160 L from shifting in the reverse direction of the insertion. At the same time, the 1 st  luer portion  144 L is fitted into the concave portion  165 L. 
         [0305]    Here, the 1st luer portion  144 L and the lock part  130 L are engaged with each other to be positioned concentrically. 
         [0306]    In addition, since the contact faces of the 1st luer portion  144 L and the concave portion  165 L of the coupling pin  160 L slip against each other in the circumferential direction, the 1st luer portion  144 L and the lock part  130 L rotate relatively to each other around the central axis of the 1st luer portion  144 L. 
         [0307]    As to the above-mentioned coinfusion port  200 L which is a luer-lock coinfusion port, on the lateral side of a port body  201 L functioning as a transfusion line or a similar flow path, a rubber valve  204  having a hole  204   a  is held in place by being covered with a cylindrical cover body  202 L. A screw thread is cut on the external periphery of the cover body  202 L to thereby form a thread groove  203 L. 
         [0308]    When connecting the syringe  100 L to the coinfusion port  200 L, the operator rotates the lock part  130 L and screws the lock part  130 L onto the thread groove  203 L while inserting the 2nd luer portion  141 L of the syringe  100 L into the hole  204   a  of the coinfusion port  200 L, as shown in  FIG. 36C , and whereby the syringe  100 L is securely connected to the coinfusion port  200 L. 
         [0309]    When connecting the syringe  100 L to the luer-slip coinfusion port  210 L, the operator is able to rapidly connect the syringe  100 L, to which the lock part  130 L is not attached, to a coinfusion port  210 L by inserting the 2nd luer portion  141 L into the hole  204   a  of the coinfusion port  210 L, as shown in  FIG. 38 . 
         [0310]    Thus, since the syringe  100 L of the present embodiment allows for easy attachment and detachment of the lock part  130 L by insertion and pullout of the coupling pin  160 L, the syringe  100 L is smoothly connected to a luer-slip style instrument by detaching the lock part  130 L from the syringe  100 L, similarly to the case of a conventional luer-slip syringe. 
         [0311]    When the syringe  100 L is connected to an instrument in the luer-lock style, secure connection can be established by attaching the lock part  130 L to the syringe  100 L, similarly to the case of a conventional luer-lock syringe. 
         [0312]    In Embodiment 17, the 1 st  luer portion  144 L and the lock part  130 L are designed to rotate relatively to each other, however, the present invention is not limited to this. For example, the following structure may be employed: a spline parallel to the syringe axis direction (hereinafter, “the 1 st  spline) is provided on the outer surface of the 1 st  luer portion  144 L of the syringe  100 L, and another spline (hereinafter, “the 2 nd  spline”) corresponding to the 1 st  spline is provided on the concave portion  165 L of the coupling pin  160 L. Herewith, when the 1 st  luer portion  144 L is fitted into the concave portion  165 L, the 1 st  and 2 nd  splines are fitted with each other so that the 1 st  luer portion  144 L is positionally fixed in relation to the concave portion  165 L. 
         [0313]    In this case, although the syringe  100 L and the lock part  130 L cannot rotate relative to each other, the above-mentioned nut can be screwed by rotating the entire syringe  100 L while inserting the 2 nd  luer portion  141 L into a target location since the lock part  130 L and the 1 st  luer portion  144 L are in a concentric configuration. 
         [0314]    Note also that, although in Embodiment 17 the lock part  130 L of the syringe  100 L is a nut that engages with an instrument such as a coinfusion port, this is merely an example and the part does not have to be a nut. 
         [0315]    For instance, as in Embodiment 18 shown in  FIG. 39 , a lock part  132 L having claw portions  133   a  and  133   b  may be used instead of the lock part  130 L having a thread. 
         [0316]    In this case, the change in the locking mechanism of the syringe necessitates a change in the structure of the engaging portion of the luer-lock coinfusion port. A coinfusion port  220 L having two L-shaped grooves  231   a  is one example of such a structural change. 
         [0317]    Note that, although the coupling pin  160 L is substantially U-shaped, this is merely an example. If a pin fulfills a similar function, i.e. enabling the lock part  130 L and the luer part  140 L to be fixed at a determined position, the pin may take any shape. 
         [0318]    For example, a coupling pin  180  of Embodiment 19 shown in  FIG. 40  (corresponding to  FIG. 36D ) may be used. Here, a lock part  170 L has been formed by partially revising the cross-sectional shape of the lock part  130 L so that the lock part  170 L serves the function fulfilled by one of the two extending portions  163 L of the coupling pin  160 L, and the coupling pin  180 L has only one extending portion  163 L. 
       INDUSTRIAL APPLICABILITY 
       [0319]    The connector-attached syringes, connectors used for syringes, and syringes of the present invention can be used to apply liquid medication to patients and collect blood in medical practices. 
         [0320]    The connector-attached syringes and connectors of the present invention are adaptable for both luer-slip and luer-lock style ports, providing a cost reduction to the users. 
         [0321]    The present invention is applicable to manufacturing medical syringes used in medical practices in which various types of connection ports are used.