Patent Publication Number: US-9898105-B2

Title: Position indicator

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to a position indicator used with a position detecting sensor. 
     2. Description of the Related Art 
     The following position indicator has been provided as a position indicator used with a position detecting sensor in which position detection is performed. Specifically, the position indicator has a configuration of so-called full-duplex communication, in which a signal input channel and a signal output channel independently exist, and thereby has a high affinity with the position detecting sensor. Furthermore, the position indicator has high general versatility and can ensure predetermined waveform correlativity between an input signal and an output signal (refer to Japanese Patent No. 4683505 (Patent Document 1)). 
       FIG. 10  is a diagram for explaining the conceptual configuration of a position indicator  301  of this Patent Document 1 and the processing operation thereof in a generalizing manner and shows a state in which the position indicator  301  is located over a plate surface of a capacitive position detecting sensor  302 . 
     In the position indicator  301 , a signal processing circuit  304  and a battery  305  that provides a supply voltage to the signal processing circuit  304  are housed in a hollow part of a tubular chassis  303  that has an opening on one end in the axial center direction and is formed into a pen shape. The chassis  303  is formed by covering at least a part which an operator holds this position indicator in the outer circumferential surface of a tubular body formed of, e.g., an insulating material such as a synthetic resin by, e.g., an electrical conductor such as a metal. 
     As shown in a partially enlarged view of  FIG. 11 , the opening side of the chassis  303  of this position indicator  301  is formed as a tapered part  303   a  that gradually becomes thinner toward the tip, and a peripheral electrode  306  that is formed into a ring shape and is formed of a metal having electrical conductivity is attached to the outer circumferential side of the tapered part  303   a . Furthermore, a central electrode  307  is housed in the hollow part of the chassis  303  of the position indicator  301  in a state in which a tip part  307   a  of the central electrode  307  protrudes from the opening to the outside as shown in  FIG. 11 . The tip of the central electrode  307  is covered by an elastic protective member  307   b  formed of electrically-conductive elastic rubber or the like so that an indication input surface of the position detecting sensor  302  may be prevented from being scratched and a contact area with the indication input surface may be made larger. 
     In this case, in the direction orthogonal to the axial center direction of the position indicator  301 , the tapered part  303   a  of the chassis  303  intervenes between the peripheral electrode  306  and the central electrode  307 . The peripheral electrode  306  and the central electrode  307  are insulated from each other by this tapered part  303   a  of the chassis  303 . Moreover, in the direction orthogonal to the axial center direction of the position indicator  301 , a shield member  308  for effectively preventing electrical interference between the peripheral electrode  306  and the central electrode  307  is provided between the peripheral electrode  306  and the central electrode  307 . The shield member  308  is formed of a tubular conductor composed of an electrically-conductive metal having an insulating layer  308   a  formed on the inner wall surface and the central electrode  307  is housed in this tubular conductor. Therefore, the central electrode  307  is configured to be surrounded by the shield member  308  and the shield member is connected to the ground (earth: the same hereinafter) to make a capacitive shield. 
     When this position indicator  301  is disposed over the position detecting sensor  302 , as shown in  FIG. 10 , the peripheral electrode  306  is coupled to the position detecting sensor  302  via capacitance C 1  and the central electrode  307  is also coupled to the position detecting sensor  302  via capacitance C 2 . 
     Meanwhile, an alternating current (AC) signal flows in the position detecting sensor  302  and thus this AC signal is supplied as a current signal to the signal processing circuit  304  via the capacitance C 1  and the peripheral electrode  306 . This signal processing circuit  304  executes processing of intensifying a signal, such as amplifying an input AC signal, and supplies an AC signal that is an output signal of the signal processing result to the central electrode  307 . When the position indicator  301  exists over the position detecting sensor  302 , the central electrode  307  is coupled to the position detecting sensor  302  via the capacitance C 2  and thus the AC signal is returned from the position indicator  301  to the position detecting sensor  302 . 
     Because the intensified AC signal is returned from the position indicator  301  to the position detecting sensor  302  in the above manner, the position detecting sensor  302  can detect the position indicated by the position indicator  301  with high sensitivity. 
     In this case, when the voltage of the AC signal of the position detecting sensor  302  in the transmitting conductor is defined as V and the voltage of the central electrode  307  of the position indicator  301  is defined as e and capacitance between the peripheral electrode  306  and the central electrode  307  is defined as C 3  (see  FIG. 10 ), a relationship of
 
 e≦C 1 /C 3 ·V  
 
is satisfied. Therefore, to increase the voltage e of the central electrode  307 , it is advantageous that the capacitance C 3  between the peripheral electrode  306  and the central electrode  307  is as low as possible.
 
     In the position indicator  301 , the capacitance C 3  between the peripheral electrode  306  and the central electrode  307  is made low by interposing the shield member  308  between the peripheral electrode  306  and the central electrode  307  to make the coupling between them as small as possible. This can increase the voltage e and efficiently enhance the sensitivity. 
     As described in Patent Document 1, it is also possible for the position indicator  301  to be configured to receive the AC signal from the position detecting sensor  302  by the central electrode  307  and transmit the AC signal resulting from the signal intensification by the signal processing circuit  304  from the peripheral electrode  306 . 
     Recently, along with an increase in the preciseness of the indicated position in the position detecting sensor, demands for reduction in the thickness of the core body (central electrode) of the position indicator and hence for reduction in the thickness of the position indicator are increasing. 
     However, in the position indicator  301  of the above-described Patent Document 1, an insulating part (tapered part  303   a  of the chassis  303 ), a shield part (shield member  308 ), and an insulating part (insulating layer  308   a ) need to be provided between the central electrode  307  and the peripheral electrode  306  and it is difficult to satisfy the demands for the thickness reduction. 
     Furthermore, if a writing pressure being applied to the position indicator can be detected in the position detecting sensor, e.g., processing of changing the line width in line drawing by a user with use of the position indicator according to the writing pressure can be executed, which is convenient. Therefore, it is desirable for the position indicator to be configured to include a writing pressure detecting measure that detects the writing pressure applied to the core body (central electrode) and transmit writing pressure information detected by this writing pressure detecting measure to the position detecting sensor. 
     To detect the writing pressure by such a writing pressure detecting measure, the writing pressure applied to the core body (central electrode) of the position indicator needs to be transmitted to the writing pressure detecting measure. For this purpose, a configuration for allowing the core body (central electrode) of the position indicator to move in the axial center direction of the position indicator and surely transmitting the writing pressure is necessary. 
     In this case, the position indicator needs to have a configuration to ensure a predetermined thickness as the thickness of the core body in order to surely transmit the writing pressure and allow the central electrode to move in the axial center direction of the position indicator while having a structure to make the coupling between the peripheral electrode  306  and the central electrode  307  as small as possible. Thus, it is more difficult to employ the configuration designed in consideration of thickness reduction. 
     SUMMARY OF THE INVENTION 
     An object of this disclosure is to provide a position indicator that can solve the above problems. 
     To solve the above-described problems, in this disclosure, 
     a position indicator is provided that includes a first electrode receiving an AC signal from a position detecting sensor and a second electrode transmitting an AC signal to the position detecting sensor and makes position indication to the position detecting sensor. The position indicator includes 
     a tubular chassis that is formed into a pen shape and has an opening on one end in an axial center direction, 
     a central electrode that is provided in the chassis such that one end protrudes from the opening of the chassis to an outside, and is formed of a bar-shaped electrically-conductive member forming one of the first electrode and the second electrode, 
     a peripheral electrode that is provided to surround the central electrode on a side of the opening and is formed of an electrically-conductive member forming another of the first electrode and the second electrode, and 
     a shield member that is provided between the central electrode and the peripheral electrode and has a tubular part that is formed of an electrically-conductive member and has a hollow part housing at least a part surrounded by the peripheral electrode in the central electrode, 
     wherein the shield member includes an insulating layer formed on an inner wall surface and an outer wall surface of the tubular part corresponding to the part surrounded by the peripheral electrode in the central electrode, and the tubular part is electrically connected to the ground. 
     In the position indicator according to this disclosure with the above-described configuration, in the direction orthogonal to the axial center direction, the insulating layer is formed at least on the inner wall surface and the outer wall surface of the tubular part formed of the electrically-conductive member corresponding to the part surrounded by the peripheral electrode in the central electrode is interposed between the central electrode and the peripheral electrode. By this shield member, the insulation and shield (mainly capacitive shield) between the central electrode and the peripheral electrode are realized. 
     Therefore, in the position indicator according to this disclosure, the configuration can be made in which only the shield member includes the insulating layer formed on the inner wall surface and the outer wall surface is disposed between the central electrode and the peripheral electrode. Thus, thickness reduction of the position indicator can be easily realized. 
     Furthermore, in this disclosure, it is more preferable to employ a configuration in which the tubular part of the shield member is composed of aluminum and the insulating layer is formed at least on the inner wall surface and the outer wall surface corresponding to the part surrounded by the peripheral electrode in the central electrode by performing alumite processing on the aluminum. 
     According to this disclosure, it is possible to make the configuration in which only the shield member including the insulating layer formed at least on the inner wall surface and the outer wall surface corresponding to the part surrounded by the peripheral electrode in the central electrode is disposed between the central electrode and the peripheral electrode. Thus, thickness reduction of the position indicator can be easily realized. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of an example of an electronic apparatus with which a position indicator according to an embodiment of this disclosure is used; 
         FIG. 2  is a diagram showing a configuration example of a position detecting sensor used with a position indicator according to an embodiment of this disclosure; 
         FIG. 3  is a partial sectional view of a configuration example of a position indicator according to an embodiment of this disclosure; 
         FIG. 4  is a circuit diagram of a position indicator according to an embodiment of this disclosure; 
         FIG. 5  is a partial sectional view of a position indicator according to an embodiment of this disclosure; 
         FIG. 6  is a perspective view of exemplary components housed inside a chassis of a position indicator according to an embodiment of this disclosure in an assembled state; 
         FIG. 7  is an exploded perspective view of the components shown in  FIG. 6 ; 
         FIG. 8  is a diagram showing the components shown in  FIG. 7  in an assembled state; 
         FIG. 9  is a sectional view along line A-A in  FIG. 6 ; 
         FIG. 10  is a circuit diagram of a conventional position indicator; and 
         FIG. 11  is a diagram showing part of a conventional position indicator. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the position indicator according to this disclosure will be described below with reference to the drawings. 
       FIG. 1  shows one example of a tablet information terminal  200  as an example of an electronic apparatus with which a position indicator  100  according to an embodiment of this disclosure is used. In this example, the tablet information terminal  200  has a display screen  200 D of a display device such as a liquid crystal display (LCD) and has a capacitive position detecting sensor  201  over the display screen  200 D (on the front surface side). 
     [Configuration Example of Position Detecting Sensor  201 ] 
     The capacitive position detecting sensor  201  of this example is a mutual capacitive position detecting sensor that has sensor electrodes composed of an input electrode and an output electrode and that detects a change in a coupling capacitance at a point touched by the position indicator  100  as described below. 
     The capacitive position detecting sensor  201  of this example will be described with reference to  FIG. 2 . Specifically, as shown in  FIG. 2 , the position detecting sensor  201  of this example is composed of a sensor unit  210 , a transmitting unit  211 , and a receiving unit  212 . The sensor unit  210  includes plural, in this example 64, transmitting conductors  213 Y 1 ,  213 Y 2 , . . . ,  213 Y 64  that extend along the horizontal direction of the indication input surface (X-axis direction) and have a straight line shape and plural, in this example 64, receiving conductors  214 X 1 ,  214 X 2 , . . . ,  214 X 64  that are orthogonal to the transmitting conductors  213 Y 1  to  213 Y 64  and extend along the vertical direction of the indication input surface (Y-axis direction). The plural transmitting conductors  213 Y 1  to  213 Y 64  are disposed at equal intervals in the Y-axis direction and are connected to the transmitting unit  211 . The plural receiving conductors  214 X 1  to  214 X 64  are disposed at equal intervals in the X-axis direction and are connected to the receiving unit  212 . 
     In this specification, in a description of the transmitting conductors, they will be referred to as the transmitting conductors  213 Y when there is no need to discriminate them among the  64  transmitting conductors  213 Y 1  to  213 Y 64 . Similarly, in a description of the receiving conductors, they will be referred to as the receiving conductors  214 X when there is no need to discriminate them among the  64  receiving conductors  214 X 1  to  214 X 64 . 
     The plural transmitting conductors  213 Y are formed on the lower surface of a substrate for example. The plural receiving conductors  214 X are formed on the upper surface of the substrate. Therefore, the plural transmitting conductors  213 Y and the plural receiving conductors  214 X have a placement relationship in which they are disposed opposed to each other at a predetermined interval and are orthogonal to each other, and form plural intersections (cross-points). Furthermore, the transmitting conductor  213 Y and the receiving conductor  214 X are coupled to each other via a predetermined capacitance at each cross-point. 
     The transmitting unit  211  supplies a predetermined AC signal to the transmitting conductors  213 Y. In this case, the transmitting unit  211  may supply the same AC signal to the plural transmitting conductors  213 Y 1 ,  213 Y 2 , . . . ,  213 Y 64  while sequentially switching the transmitting conductor one by one. Alternatively, the transmitting unit  211  may simultaneously supply plural AC signals different from each other to the plural transmitting conductors  213 Y 1 ,  213 Y 2 , . . . ,  213 Y 64 . Alternatively, the plural transmitting conductors  213 Y 1 ,  213 Y 2 , . . . ,  213 Y 64  may be divided into plural groups and AC signals different on each group basis may be used. 
     The receiving unit  212  detects a signal component obtained by transmission of the AC signal supplied to the transmitting conductor  213 Y to each of the receiving conductors  214 X 1 ,  214 X 2 , . . . ,  214 X 64  via the predetermined capacitance. If the coupling capacitance between the transmitting conductor  213 Y and the receiving conductor  214 X is equal at all cross-points, a received signal at a predetermined level is detected in the receiving unit  212  from all receiving conductors  214 X 1 ,  214 X 2 , . . . ,  214 X 64  in the sensor unit  210  when the position indicator  100  is not disposed over the sensor unit  210 . 
     On the other hand, when the position indicator  100  makes contact with the sensor unit  210 , the transmitting conductor  213 Y and the receiving conductor  214 X configuring the cross-point at the contact position and the position indicator  100  are coupled to each other via capacitance. That is, the capacitance changes due to the position indicator  100 , so that the received signal level obtained from the receiving conductor  214 X of the cross-point at which the position indicator  100  exists changes compared with the received signal level of the other cross-points. 
     The receiving unit  212  detects the receiving conductor  214 X in which the change in the signal level of the received signal is caused among the plural receiving conductors  214 X 1 ,  214 X 2 , . . . ,  214 X 64  to detect the position of the position indicator  100 . Then, a control unit (not shown) of the position detecting sensor  201  detects the cross-point with which the position indicator  100  is in contact by detecting the transmitting conductor  213 Y to which the AC signal is being supplied from the transmitting unit  211  and the receiving conductor  214 X from which the change in the signal level of the received signal is detected in the receiving unit  212 . 
     Also, when not the position indicator  100  but a finger gets close to or makes contact with the sensor unit  210 , the position detecting sensor  201  can detect the cross-point the finger gets close to or contact with. In this case, part of the AC signal supplied to the transmitting conductor  213 Y flows to the ground via the finger or the human body of the user and thus the signal level of the received signal of the receiving conductor  214 X configuring the cross-point at which the finger exists changes. Therefore, by detecting this change in the signal level of the received signal, the receiving unit  212  can detect the receiving conductor  214 X configuring the cross-point at which the finger exists. 
     Also, in the case of the position indicator  100  having a pen shape (stylus shape), the position detecting sensor  201  can detect the indicated position in the sensor unit  210  similarly to the principle of the position detection of the finger. However, in the case of the position indicator  100  having a pen shape, the contact area with the position detecting sensor  201  is smaller than in the case of the finger. Thus, the coupling capacitance is lower and the detection sensitivity of the position detection in the position detecting sensor  201  is lower. 
     However, in the case of the position indicator  100  of this embodiment, the AC signal from the position detecting sensor  201  is received and processed by the signal processing circuit to intensify the signal and then the resulting signal is returned to the position detecting sensor  201  as described above. This enables the position detecting sensor  201  to detect a contact position of the position indicator  100  with high sensitivity. 
     [Configuration Example of Position Indicator  100  of Embodiment] 
     &lt;Outline of Configuration Example of Position Indicator  100 &gt; 
     An overview of the position indicator  100  according to an embodiment will be described with reference to  FIGS. 3 and 4 . This position indicator  100  includes a tubular chassis  1  composed of an electrically-conductive material, specifically, e.g., steel special use stainless (SUS). At an opening of this chassis  1  on one end on a pen tip side of the pen shape thereof, a peripheral electrode  2  composed of an electrically-conductive material, specifically, e.g., SUS, is provided with the intermediary of an insulating sleeve  3 . The insulating sleeve  3  is to insulate the electrically-conductive chassis  1  from the peripheral electrode  2  and is composed of, e.g., an insulating resin. 
     As shown in  FIG. 4 , inside the one end on the pen tip side of the chassis  1 , a central electrode  5  is disposed in a state of being housed in a shield member  6 . The shield member  6  is to shield the central electrode  5  and ensure insulation between the central electrode  5  and the peripheral electrode  2 . In this case, from the opening at one end part on the pen tip side of the chassis  1 , a tip part  5   a  of the central electrode  5  protrudes to the outside and a tip part  6   a  of the shield member  6  is exposed to the outside for example. 
       FIG. 3  is a diagram showing a state in which part of the tubular chassis  1  of the position indicator  100  of this embodiment is represented as a section and part of the hollow part of the chassis  1  is exposed to the outside. As shown in  FIG. 3 , the side opposite to the pen tip side of the chassis  1  is closed by a lid part  4  and a printed board  21  on which a signal processing circuit and so forth (not shown in  FIG. 3 ) are disposed is housed in a hollow part  101   a  of the tubular chassis  1 . Furthermore, a battery  22  that provides a supply voltage to the signal processing circuit and so forth is housed between the printed board  21  and the lid part  4 . In this example, the lid part  4  is allowed to be removed so that the battery  22  can be replaced. 
       FIG. 4  is a diagram showing a circuit example disposed on the printed board  21  of the position indicator  100  of this embodiment and the electrical connection relationship among the respective components in the position indicator  100 . As shown in  FIG. 4 , in the position indicator  100  of this embodiment, a signal processing circuit  401 , an integrated circuit (IC)  402 , and a wireless transmission circuit  403  (i.e., a transmitter) are provided on the printed board  21 . A power supply circuit that provides a supply voltage from the voltage from the battery  22  to these signal processing circuit  401 , IC  402 , and wireless transmission circuit  403  is also provided on the printed board  21  although not shown in  FIG. 4 . 
     In this embodiment, the central electrode  5  is configured to be electrically connected to the input terminal of the signal processing circuit  401  and the output terminal of the signal processing circuit  401  is configured to be electrically connected to the peripheral electrode  2 . In this example, the signal processing circuit  401  carries out phase inversion on an AC signal (current signal) input via the central electrode  5  and then performs boosting (multiplication) by using a transformer, for example, to intensify the signal and supply the resulting signal to the peripheral electrode  2  as a voltage signal. 
     Therefore, the AC signal returned from the peripheral electrode  2  of the position indicator  100  to the sensor unit  210  of the position detecting sensor  201  is a reverse-phase signal resulting from the intensification of the AC signal supplied to the transmitting conductor  213 Y. Thus, the position indicator  100  functions to increase the change in the AC signal in the received signal of the receiving conductor  214 X of the position detecting sensor  201 . This enables the position detecting sensor  201  to detect the contact position of the position indicator  100  with high sensitivity. 
     In this embodiment, the chassis  1  of the position indicator  100  is formed of SUS as an electrically-conductive material and is connected to an earth conductor (not shown) formed on the printed board  21 , on which the signal processing circuit  401  is provided. Therefore, the AC signal supplied to the transmitting conductors  213 Y in the position detecting sensor  201  flows to the ground via the chassis  1  of the position indicator  100  and the human body of the user (see a dotted line in  FIG. 4 ), which allows further stabilization of the signal detection operation. 
     As shown in  FIG. 4 , in this embodiment, the shield member  6  has a configuration obtained by covering a tubular body  61  composed of an electrically-conductive material by an insulating layer  62  across its whole surface including the outer wall surface and inner wall surface. However, as described later, part of the shield member  6  is formed as a part at which the insulating layer  62  is not formed so that an outer wall surface  61   a  of the tubular body  61  of the electrically-conductive material may be exposed at this part. This part at which the outer wall surface  61   a  is exposed is used as a terminal part for an electrical connection to the earth conductor on the printed board  21 . Electrical insulation between the central electrode  5  and the peripheral electrode  2  is realized by the insulating layer  62  of the shield member  6 . In addition, a capacitive shield between the central electrode  5  and the peripheral electrode  2  is realized by the connection of the tubular body  61  of the electrically-conductive material in the shield member  6  to the earth conductor. 
     Furthermore, in this embodiment, a writing pressure detecting unit  10  that detects a pressure applied to the central electrode  5  forming the core body, i.e., writing pressure, is provided in the hollow part  101   a  of the chassis  1  of the position indicator  100  as shown in  FIG. 4 . As described later, this writing pressure detecting unit  10  has a configuration based on a variable-capacitance capacitor Cv that receives the writing pressure applied to the central electrode  5  via a pressure transmitting member  7  and changes a capacitance of the variable-capacitance capacitor Cv. As shown in  FIG. 4 , the central electrode  5  and the pressure transmitting member  7  are joined to each other and are housed in a slidable state in the hollow part of the tubular body  61  of the shield member  6 . 
     Both electrodes of the variable-capacitance capacitor Cv formed of the writing pressure detecting unit  10  are connected to the IC  402 . The IC  402  calculates the writing pressure applied to the position indicator  100  from the value of the capacitance of the variable-capacitance capacitor Cv. Then, the IC  402  converts the calculated writing pressure to transmission data and transmits it to the position detecting sensor  201  via the wireless transmission circuit  403 . The wireless transmission circuit  403  is formed of, e.g., a near-distance wireless transmission measure of the Bluetooth (registered trademark) standard or the like. The position detecting sensor  201  receives and decodes this transmission data of the writing pressure to detect the writing pressure applied to the position indicator  100 . 
     &lt;Detailed Configuration Example of Major Part of Position Indicator  100 &gt; 
       FIG. 5  is a sectional view showing a detailed configuration example of the pen tip side of the position indicator  100  of this embodiment and corresponds to the part that is not shown as the section in  FIG. 3 . For easier understanding,  FIG. 5  shows a state obtained by cutting a perspective view of the pen tip side of the position indicator  100  by a plane including the central axis position of the tubular body forming the chassis  1 . 
       FIG. 6  is a diagram showing a component group housed in the hollow part of the tubular chassis  1  in an assembled state.  FIG. 7  is an exploded perspective view of major components in the component group in this  FIG. 6 .  FIG. 8  is a diagram showing a state in which the major components shown in  FIG. 7  are assembled and  FIG. 9  is a sectional view along line A-A in  FIG. 6 . 
     As shown in  FIG. 5 , the insulating sleeve  3  is formed into a truncated cone shape that has an outer circumferential surface  3   a  formed into a tapered shape to gradually become thinner toward the pen tip side and has a through-hole  3   b  through which the shield member  6  to shield the central electrode  5  is inserted. The diameter of the pen tip side of this through-hole  3   b  is set slightly larger for joining to the peripheral electrode  2 . In addition, a screw part  3   c  for screwing the peripheral electrode  2  is formed in the inner wall surface of the pen tip side of the through-hole  3   b . Furthermore, the insulating sleeve  3  has a protruding part  3   d  that protrudes from the end surface of the larger-diameter part on the side opposite to the pen tip side in the axial center direction. This protruding part  3   d  is press-fitted into the opening end part of the pen tip side of the tubular chassis  1  and thereby the insulating sleeve  3  is fixed to the chassis  1 . Symbol  3   e  denotes a decorative ring and it is clamped and fixed between the insulating sleeve  3  and the chassis  1  when the insulating sleeve  3  is press-fitted and fixed to the chassis  1 . 
     The peripheral electrode  2  is composed of SUS as an example of an electrically-conductive material and is formed into a truncated cone shape that has an outer circumferential “surfaced formed”into a tapered shape continuously with the outer circumferential surface  3   a  of the insulating sleeve  3  and has a through-hole  2   b  through which the shield member  6  in which the central electrode  5  is housed is inserted. Furthermore, a protruding part  2   c  that protrudes in the axial center direction is provided on the side opposite to the pen tip side of the peripheral electrode  2 . On this protruding part  2   c  of the peripheral electrode  2 , a screw part  2   d  screwed to the screw part  3   c  of the insulating sleeve  3  is formed. 
     The through-hole  2   b  of the peripheral electrode  2  is formed such that the diameter of its part on the pen tip side is the minimum inner diameter. As this minimum inner diameter, a diameter slightly larger than the outer diameter of the part of the shield member  6  on the pen tip side is selected. The inner diameter of the through-hole  2   b  of the peripheral electrode  2  on the side of the screw part  2   d  is set larger than the minimum inner diameter. As described later, a terminal piece  9  (see  FIG. 6 ) for an electrical connection between the signal processing circuit disposed on the printed board  21  and the peripheral electrode  2  is allowed to be located in the space between this larger-inner-diameter part of the through-hole  2   b  and the shield member  6 . 
     As shown in  FIGS. 5, 7, and 8 , the central electrode  5  includes a core body  51  composed of an electrically-conductive material, specifically, e.g., a metal, whose diameter is set to, e.g., 1.9 mm. Furthermore, in this embodiment, in the central electrode  5 , about half of the core body  51  on the pen tip side is covered by a protective member  52  composed of an insulating material, specifically polyoxymethylene (POM) in this example. This part of the core body  51  covered by the protective member  52  becomes a state in which the peripheral electrode  2  is located around this part when being assembled as the position indicator  100 . As shown in  FIGS. 5 and 8 , the core body  51  is formed such that its tip part  51   a  has a spherical shape and the protective member  52  is formed to cover the whole of this spherical tip part  51   a  of the core body  51  and forms the tip part  5   a  of the central electrode  5 . This protective member  52  has roles in preventing scratching of the indication input surface of the position detecting sensor  201  and increasing the contact area with the indication input surface. Furthermore, particularly in this embodiment, the protective member  52  has a role in strengthening insulation from the shield member  6  and the peripheral electrode  2 . 
     In this embodiment, the tubular body  61  composed of an electrically-conductive material forming the shield member  6  is composed of alumite-processed aluminum. Furthermore, as shown in  FIGS. 5 and 8 , the insulating layer  62  is formed of an alumite coat formed to cover the whole surface of the tubular body  61  including the outer wall surface  61   a  and an inner wall surface  61   b.    
     However, the alumite processing of the tubular body  61  is performed such that, at a terminal part  63 , the insulating layer  62  is not formed and the outer wall surface  61   a  of the tubular body  61  composed of the electrically-conductive material is exposed as shown in  FIGS. 6 and 7 . The terminal part  63  of the tubular body  61  is electrically connected to the earth conductor (ground) of the printed board  21  and an electric field shield of the central electrode  5  is formed by the tubular body  61 . This terminal part  63  can be formed by masking the corresponding part when alumite processing of the tubular body  61  is performed for example. Alternatively, after the alumite processing, the alumite coat at the terminal part  63  may be removed to expose the outer wall surface  61   a  of the tubular body  61 . 
     In this embodiment, as described by using  FIG. 4 , in the hollow part of the tubular body  61  of the shield member  6 , the central electrode  5  and the pressure transmitting member  7  joined to each other are housed movably in this hollow part in the axial center direction of the central electrode  5 . As the pressure transmitting member  7 , a member having a larger diameter than the central electrode  5  is used. 
     For this reason, as shown in  FIGS. 5 and 8 , the tubular body  61  of the shield member  6  is configured to have a smaller-diameter part  64  having such an inner diameter as to house the central electrode  5  movably in the axial center direction mainly on the pen tip side and a larger-diameter part  65  having such an inner diameter as to house the pressure transmitting member  7  movably in the axial center direction on the opposite side to the pen tip side. 
     As the inner diameter of the hollow part of the smaller-diameter part  64 , a diameter slightly larger than the outer diameter of the central electrode  5  (diameter of the part where the protective member  52  is formed on the core body  51 ) is selected. Furthermore, as the inner diameter of the larger-diameter part  65 , a diameter slightly larger than the maximum diameter of the pressure transmitting member is selected. Therefore, in the hollow part of the tubular body  61 , a step part  66  is formed at the part at which the change from the smaller-diameter part  64  to the larger-diameter part  65  is made. Furthermore, also on the outer circumferential side surface of the tubular body  61 , a step part  67  is formed at the part at which the change from the smaller-diameter part  64  to the larger-diameter part  65  is made. 
     The pressure transmitting member  7  is formed of an insulating material, specifically a resin in this example. As shown in  FIGS. 5, 7, and 8 , the pressure transmitting member  7  has a core body fitting part  71  into which an end part  51   b  of the core body  51  of the central electrode  5  is fitted and a protruding part  72  fitted into the writing pressure detecting unit  10 . The core body fitting part  71  of the pressure transmitting member  7  is configured by forming a recess  71   a  into which the end part  51   b  of the core body  51  of the central electrode  5  is inserted in a circular columnar member. As shown in  FIG. 7 , at part of the side circumferential surface of this core body fitting part  71 , a slit  71   b  obtained by notching the sidewall of the recess  71   a  in the axial center direction from the opening side to the bottom part is formed. As shown in  FIGS. 5 and 8 , the protruding part  72  of the pressure transmitting member  7  is joined to the writing pressure detecting unit  10  for transmitting a writing pressure thereto. 
     As shown in  FIGS. 7 and 8 , in the recess  71   a , a terminal piece  73  for an electrical connection between the central electrode  5  and the signal processing circuit  401  of the printed board  21  is disposed. This terminal piece  73  is formed of a metal plate and, as shown in  FIGS. 7 and 8 , has a pair of first terminal pieces  73   a  that are disposed opposed to each other in a direction orthogonal to the axial center direction and are formed to extend along the axial center direction in the recess  71   a  and a second terminal piece  73   b  disposed to protrude in a direction orthogonal to the outer circumferential side surface of the core body fitting part  71  of the pressure transmitting member  7  through the slit  71   b . The pair of first terminal pieces  73   a  are formed elastically displaceably in the direction orthogonal to the axial center direction and are disposed such that the interval thereof is the same as or somewhat smaller than the diameter of the core body  51 . 
     The core body  51  of the central electrode  5  is joined to the pressure transmitting member  7  by insertion (press-fitting) of its end part  51   b  into the recess  71   a  of the core body fitting part  71  of the pressure transmitting member  7 , and a writing pressure applied to the core body  51  is transmitted to the writing pressure detecting unit  10  to be described later via the pressure transmitting member  7 . Specifically, the end part  51   b  of the core body  51  of the central electrode  5  is press-fitted into between the pair of first terminal pieces  73   a  in the recess  71   a  of the core body fitting part  71  against the elastic displacement force of them. Along with this, the core body  51  of the central electrode  5  is elastically clamped by the pair of terminal pieces  73   a  as shown in  FIG. 8 . Therefore, the central electrode  5  is locked to the pressure transmitting member  7  and is set to a state in which the locking to the pressure transmitting member  7  is not released unless the central electrode  5  is pulled out by a predetermined force. 
     The unit obtained by the joining of the central electrode  5  and the pressure transmitting member  7  in the above manner is housed movably in the axial center direction in the tubular body  61  of the shield member  6 . The core body fitting part  71  of the pressure transmitting member  7  engages with the step part  66  of the hollow part of the tubular body  61  of the shield member  6 , which prevents the central electrode  5  and the pressure transmitting member  7  from dropping off to the pen tip side. However, when a force is applied to pull out only the central electrode  5 , the elastic clamping of the end part  51   b  of the core body  51  by the first terminal pieces  73   a  is released and the central electrode  5  can be pulled out from the pressure transmitting member  7 . That is, a configuration enabling replacement of the central electrode  5  is made. 
     Next, the writing pressure detecting unit  10  will be described below. As the writing pressure detecting unit  10  of this example, a writing pressure detecting measure having a known configuration described in patent document, Japanese Patent Laid-Open No. 2011-186803 is used for example. The writing pressure detecting unit  10  configures a variable-capacitance capacitor whose capacitance changes according to the writing pressure applied to the central electrode  5 . 
     As shown in  FIGS. 5 and 8 , the writing pressure detecting unit  10  of this example is formed by housing plural components, a dielectric  12 , an electrically-conductive member  13 , an elastic member  14 , a holding member  15 , and a terminal member  16 , in a housing member  11  composed of an insulating material, specifically, e.g., a resin. The terminal member  16  forms a first electrode of the variable-capacitance capacitor configuring the writing pressure detecting unit  10 . Furthermore, the electrically-conductive member  13  and the elastic member  14  are electrically connected to each other and form a second electrode of the variable-capacitance capacitor. 
     The housing member  11  is formed of a tubular body having a hollow part and has a configuration to arrange the holding member  15 , the elastic member  14 , the electrically-conductive member  13 , the dielectric  12 , and the terminal member  16  in the axial center direction and house them in the hollow part. The dielectric  12  and the terminal member  16  are fixed so as not to move in the axial center direction relative to the housing member  11 . 
     The holding member  15  is provided movably in the axial center direction relative to the housing member  11 . At the end surface of this holding member  15  on the pen tip side, a recess  15   a  into which the protruding part  72  of the pressure transmitting member  7  is fitted is made. By the press-fitting of the protruding part  72  of the pressure transmitting member  7  into this recess  15   a  of the holding member  15 , the whole of the central electrode  5 , the pressure transmitting member  7 , and the holding member  15  is allowed to move in the axial center direction according to the writing pressure applied to the central electrode  5 . 
     At the end surface of the holding member  15  on the opposite side to the end surface at which the recess  15   a  is formed, the electrically-conductive member  13  is joined and held. This electrically-conductive member  13  is formed of a member that has electrical conductivity and is elastically deformable, specifically, e.g., an elastic member such as a silicone conductive rubber or a pressure conductive rubber. The elastic member  14  is formed of, e.g., a coil spring having electrical conductivity. The elastic member  14  has a winding part having elasticity and a terminal piece (not shown) at one end part of this winding part, and has a connecting part  14   a  at the other end part of the winding part. 
     The elastic member  14  is combined to surround the electrically-conductive member  13  held by the holding member  15  by its winding part. At this time, an end surface of the electrically-conductive member  13  makes contact with the connecting part  14   a  of the elastic member  14  having electrical conductivity and becomes in a state of being electrically connected thereto. The terminal piece (not shown) at the end part on the opposite side to the connecting part  14   a  of the elastic member  14  is configured to be soldered to an electrically-conductive pattern of the printed board  21 . 
     The terminal member  16  is configured to be electrically connected to an electrically-conductive pattern of the printed board  21  (this connection is not shown). 
     In the writing pressure detecting unit  10  configured as above, when a writing pressure is applied to the central electrode  5 , this writing pressure is transmitted to the holding member  15  of the writing pressure detecting unit  10  via the pressure transmitting member  7  and the holding member  15  moves the electrically-conductive member  13  toward the dielectric  12  according to the applied writing pressure. Along with this, an end part of the electrically-conductive member  13  abuts against the dielectric  12  and the contact area with the electrically-conductive member  13  changes according to the applied writing pressure. Thus, the capacitance of the variable-capacitance capacitor formed between the first electrode and the second electrode is changed according to the applied writing pressure. 
     Then, as described above, the position indicator  100  of this embodiment detects, by the IC  402 , the writing pressure applied to the position indicator  100  from the capacitance of the variable-capacitance capacitor configuring the writing pressure detecting unit  10  and transmits information on the detected writing pressure through the wireless transmission circuit  403 . 
     [Connection Between Central Electrode  5  and Input Terminal of Signal Processing Circuit  401 ] 
     The terminal piece  73  disposed in the pressure transmitting member  7  is a member for electrically connecting the central electrode  5  to the signal processing circuit disposed on the printed board  21 . The end part  51   b  of the core body  51  of the central electrode  5  elastically makes contact with the first terminal pieces  73   a  and thereby the central electrode  5  is electrically connected to the terminal piece  73 . 
     The length of the second terminal piece  73   b  of the terminal piece  73  is set to such a length that its tip protrudes to the outside of the housing member  11  of the writing pressure detecting unit  10  as shown in  FIGS. 7 and 8 . Furthermore, as shown in  FIGS. 7 and 9 , a notch having a V-shape or a U-shape is made at the tip of this second terminal piece  73   b  of the terminal piece  73 . 
     To this V-shaped or U-shaped notch at the tip of the second terminal piece  73   b , one end of a connecting line  23  formed of, e.g., a copper line is soldered as shown in  FIGS. 8 and 9 . The other end of this connecting line  23  is connected by soldering or the like to a conductor pattern to which an input terminal of the signal processing circuit  401  provided on the printed board  21  is connected, although not shown in the diagram. 
     Because the second terminal piece  73   b  of the terminal piece  73  housed in the pressure transmitting member  7  is configured to protrude to the outside of the housing member  11  of the writing pressure detecting unit  10 , the connecting line  23  is disposed at such a position as to connect the second terminal piece  73   b  of the terminal piece  73  to the printed board  21  while bypassing the whole of the writing pressure detecting unit  10  interposed between the printed board  21  and the pressure transmitting member  7 . 
     [Connection Between Tubular Body  61  of Shield Member  6  and Earth Conductor] 
     Next, a configuration for the connection between the tubular body  61  of the shield member  6  and the earth conductor of the printed board  21  will be described. Specifically, also as described above, the tubular body  61  of the electrically-conductive material configuring the shield member  6  needs to be electrically connected to the earth conductor of the printed board  21 . The earth conductor of the printed board  21  is electrically connected to the chassis  1 . Therefore, when a user holds the chassis and operates the position indicator  100 , the earth conductor is connected to the earth (ground) via the human body and provides a favorable shield effect. 
     As shown in  FIGS. 5, 6, and 9 , in this embodiment, the shield member  6  and the writing pressure detecting unit  10  are disposed in a holder  30 . This holder  30  has a so-called dugout-like shape like a shape obtained by cutting the tubular body  61  by a plane along the axial center direction thereof. The part of the holder  30  to house the shield member  6  has a recess shape corresponding to the outer shape of the shield member  6 . Furthermore, the part to house the writing pressure detecting unit  10  has a recess shape corresponding to the outer shape of the housing member  11  of the writing pressure detecting unit. 
     As shown in  FIGS. 5 and 6 , in this example, the step part  67  formed on the side of the outer wall surface  61   a  of the tubular body  61  of the shield member  6  engages with a step part  31  formed in the holder  30  and thereby the shield member  6  is prevented from moving in the axial center direction in the holder  30 . Furthermore, the writing pressure detecting unit  10  is prevented from moving in the axial center direction by the combination of the recess corresponding to the outer shape of the writing pressure detecting unit  10  and the preventing the shield member  6  from moving in the axial center direction. Furthermore, as shown in  FIG. 5 , the holder  30  abuts against the insulating sleeve  3  to be restricted from moving toward the opening side of the chassis  1  on the pen tip side. In addition, the printed board  21  joined and fixed to this holder  30  is fixed by the lid part  4  with the intermediary of the housing part of the battery  22  and thereby the holder  30  is also restricted from moving toward the lid part  4 . 
     As shown in  FIG. 6 , in this example, at one end of the printed board  21  in the longitudinal direction, arm parts  21   a  and  21   b  extending along the longitudinal direction of the printed board  21  are formed from both end parts of the printed board  21  in a direction orthogonal to the longitudinal direction. The arm parts  21   a  and  21   b  of this printed board  21  are joined to the opening end surface of the part at which the writing pressure detecting unit  10  is housed in the holder  30  and thereby the printed board  21  is fixed to the holder  30 . 
     In this case, although not shown in the diagram, a conductor pattern to connect to the output terminal of the signal processing circuit  401  disposed on the printed board  21  is formed on the arm part  21   a  and a conductor pattern to connect to the earth conductor of the printed board  21  is formed on the arm part  21   b.    
     In this embodiment, as shown in  FIGS. 5, 6, 8, and 9 , a ring terminal piece  8  shown in  FIG. 7  is provided between the pressure transmitting member  7  and the housing member  11  of the writing pressure detecting unit  10 . In this case, the ring terminal piece  8  is formed to have substantially the same size and shape as an end surface of the tubular housing member  11 . Furthermore, the protruding part  72  of the pressure transmitting member  7  is inserted through a ring space  8   a  of the ring terminal piece  8  and the ring terminal piece  8  is clamped by a step part formed between the core body fitting part  71  and the protruding part  72  and the end surface of the housing member  11  of the writing pressure detecting unit  10 . 
     In this ring terminal piece  8 , connection protrusions  8   b  and  8   c  are formed at positions corresponding to the terminal parts  63 , at which the outer wall surface  61   a  of the tubular body  61  provided in the shield member  6  is exposed. The terminal parts  63  of the tubular body  61  are formed at two positions that are opposed to each other and are separate by an angular interval of 180 degrees. The connection protrusions  8   b  and  8   c  are formed corresponding to these two terminal parts  63 . Furthermore, in the ring terminal piece  8 , a connection protrusion  8   d  to connect to the electrically-conductive pattern connected to the earth conductor formed on the arm part  21   b  of the printed board  21  is also formed. 
     As shown in  FIGS. 6 and 9 , the connection protrusions  8   b  and  8   c  of the ring terminal piece  8  are each soldered to the outer wall surface  61   a  of the tubular body  61  exposed at the terminal part  63  of the shield member  6  in a state of being brought into contact with the outer wall surface  61   a . Furthermore, as shown in  FIGS. 6 and 9 , the connection protrusion  8   d  of the ring terminal piece  8  is soldered in a state of being connected to the earth conductor formed on the arm part  21   b  of the printed board  21 . By the above configuration, the tubular body  61  composed of an electrically-conductive material in the shield member  6  is connected to the earth conductor of the printed board  21  and an electric field shield is realized. 
     [Connection Between Peripheral Electrode  2  and Output Terminal of Signal Processing Circuit  401 ] 
     Next, a configuration for an electrical connection between the peripheral electrode  2  and the output terminal of the signal processing circuit  401  of the printed board  21  will be described. 
     Specifically, in this embodiment, as shown in  FIG. 7 , the terminal piece  9  for the peripheral electrode  2  is prepared by, e.g., a metal plate having elasticity as a component having a shape allowing elastic displacement in its plate thickness direction. On one end side of this terminal piece  9  for the peripheral electrode  2  in the longitudinal direction, a connection protrusion  9   a  connected to the conductor pattern connected to the output terminal of the signal processing circuit  401  formed on the arm part  21   a  of the printed board  21  is formed. On the other hand, a connection end part  9   b  that elastically makes contact with the inner wall surface of the peripheral electrode  2  is formed on the other end side of this terminal piece  9  for the peripheral electrode  2  in the longitudinal direction. 
     This terminal piece  9  for the peripheral electrode  2  is fixed to the holder  30  by fitting of the side of the connection protrusion  9   a  into a pocket part (not shown) formed in the holder  30 . As shown in  FIG. 6 , this terminal piece  9  for the peripheral electrode  2  is fixed along the outer wall surface of the housing recess for the shield member  6  in the holder  30 , with its longitudinal direction set to the same direction as the axial center direction. Therefore, when the peripheral electrode  2  is screwed to the insulating sleeve  3 , the inner wall surface of the peripheral electrode  2  elastically makes contact with the connection end part  9   b  of the terminal piece  9  and is electrically connected thereto. 
     [Isolation Between Connecting Line  23  and Terminal Piece  9  for Peripheral Electrode  2 ] 
     In this embodiment, the connecting line  23  for the electrical connection between the central electrode  5  and the input terminal of the signal processing circuit  401  of the printed board  21  and the terminal piece  9  for the electrical connection between the peripheral electrode  2  and the output terminal of the signal processing circuit of the printed board  21  form a signal line for a received signal and a signal line for a transmission signal, respectively. The connecting line  23  and the terminal piece  9  are both disposed along the axial center direction in such a manner as to straddle the writing pressure detecting unit  10 . For this reason, there is a fear that the transmission signal and the received signal interfere with each other and the position indicator  100  becomes incapable of stably operating. 
     In view of this point, in this embodiment, the occurrence of the interference between the transmission signal and the received signal is prevented as described below. 
     First, in the hollow part of the chassis  1  of the position indicator  100 , the placement position of the connecting line  23  as the signal line of the received signal and the placement position of the terminal piece  9  forming the signal line of the transmission signal are set at positions separate from each other by 180 degrees, which are positions separate from each other at the highest degree, in the circumferential direction of the hollow part of the chassis  1 . 
     Second, in this embodiment, the connecting line  23  as the signal line of the received signal is isolated from the terminal piece  9  and is shielded (electromagnetically shielded). Specifically, as shown in  FIGS. 5 and 9 , the connecting line  23  is covered by a copper tape  40  configured by forming an insulating coating layer  42  on one surface of a rolled copper foil  41 . At this time, the copper tape  40  is disposed along the writing pressure detecting unit  10 , with the insulating coating layer  42  located on the side of the connecting line  23 . As shown in  FIG. 9 , in this embodiment, the connecting line  23  is disposed in a groove  32  formed at part of the circumferential side surface of the holder  30  in such a manner as to bypass the writing pressure detecting unit  10  housed and held in the holder  30 . 
     Furthermore, in this embodiment, one end  41   a  of the rolled copper foil  41  is soldered to the arm part  21   b  of the printed board  21  fixed to the holder  30  and the copper tape  40  is connected to the earth conductor formed on the arm part  21   b . In this case, the length of the copper tape  40  in the circumferential direction is set to such a length as to cover an angular range of about 180 degrees from the arm part  21   b  of the printed board  21  to a position immediately before the placement position of the terminal piece  9  as shown in  FIG. 9 . Furthermore, the range covered by the copper tape  40  in the axial center direction includes the whole of the housing part for the writing pressure detecting unit  10  in the holder  30  in the axial center direction and reaches the base part of the arm part  21   b  of the printed board  21 . 
     By the above configuration, the signal line of the received signal by the connecting line  23  to connect the central electrode  5  and the input terminal of the signal processing circuit  401  and the signal line of the transmission signal by the terminal piece  9  to connect the peripheral electrode  2  and the output terminal of the signal processing circuit  401  are electrically isolated from each other by the shield based on the copper tape  40 , so that the interference between the transmission signal and the received signal is suppressed. 
     [Effects of Embodiment] 
     In the above manner, in the position indicator  100  of this embodiment, in the shield member  6 , the insulating layer  62  formed of an alumite coat is formed across the whole of the tubular body  61  including the outer wall surface  61   a  and the inner wall surface  61   b  by performing alumite processing on the whole of the tubular body  61  (excluding the terminal part  63 ) composed of aluminum. Furthermore, the aluminum as an electrically-conductive material is connected to the earth conductor of the printed board  21  at the terminal part  63  and thereby an electric field shield is realized. 
     Therefore, according to this embodiment, the insulation and shield between the central electrode  5  and the peripheral electrode  2  can be realized by only the shield member  6  and the thickness of the pen tip side can be reduced. In addition, the central electrode  5  can be configured to be covered by the whole of the shield member  6  and thus the thickness of the central electrode  5  can be further reduced. 
     Moreover, in this embodiment, the protective member  52  is provided at the part surrounded by the peripheral electrode  2  in the core body  51  forming the central electrode  5  and thus the insulation between the central electrode  5  and the peripheral electrode  2  is further strengthened. 
     Furthermore, in this embodiment, the central electrode  5  itself is not used to transmit a pressure to the writing pressure detecting unit  10  and the pressure is transmitted via the pressure transmitting member  7 . Thus, although the thickness of the central electrode  5  is reduced, an effect that a writing pressure can be surely transmitted to the writing pressure detecting unit  10  is provided by the pressure transmitting member  7 . 
     In addition, according to this embodiment, the central electrode  5  is allowed to be inserted and removed into and from the pressure transmitting member  7  and thus there is also an effect that the central electrode  5  can be replaced. 
     Moreover, in this embodiment, the signal line of the received signal by the connecting line  23  to connect the central electrode  5  and the input terminal of the signal processing circuit  401  and the signal line of the transmission signal by the terminal piece  9  to connect the peripheral electrode  2  and the output terminal of the signal processing circuit  401  are disposed in the hollow part of the chassis  1 . However, the connecting line  23  is shielded by the copper tape  40 , which provides an effect that the interference between the transmission signal and the received signal is suppressed. 
     [Other Embodiments or Modification Examples] 
     In the above-described embodiment, the central electrode  5  is used as a receiving electrode for a signal from the position detecting sensor and the peripheral electrode is used as a transmitting electrode to transmit a signal to the position detecting sensor. However, as described also at the beginning, it is also possible to make a configuration to use the central electrode as the transmitting electrode and use the peripheral electrode as the receiving electrode. 
     In the above-described embodiment, in the shield member  6 , the insulating layer  62  is formed to cover the whole surface of the tubular body  61  composed of an electrically-conductive material except the terminal part for an electrical connection. However, because it is enough that insulation between the peripheral electrode  2  and the central electrode  5  can be ensured, it suffices for the insulating layer  62  on the tubular body  61  of the shield member  6  to be formed at least in a region corresponding to the region in which the peripheral electrode  2  surrounds the central electrode  5 . 
     Similarly, it also suffices for the protective member  52 , which is formed to cover the tip part side of the core body  51  of the central electrode  5  and is composed of an insulating material, to be formed at least in a region range corresponding to the region in which the peripheral electrode  2  surrounds the central electrode  5 . 
     Furthermore, in the above-described embodiment, in the shield member  6 , the tubular body  61  is formed by aluminum and the insulating layer  62  is formed by performing alumite processing. However, the shield member  6  is not limited to this configuration and may be so configured that the whole of the tubular body  61  of an electrically-conductive material is covered by an insulating layer except the terminal part  63 . 
     Moreover, in the above-described embodiment, in the writing pressure detecting unit  10 , the variable-capacitance capacitor whose capacitance changes according to the writing pressure is used by interposing a dielectric between the first electrode and the second electrode and allowing one of the first electrode and the second electrode to move in the axial center direction according to the writing pressure. However, the writing pressure detecting unit  10  is not limited to this configuration. For example, it is also possible to configure the writing pressure detecting unit  10  by using a semiconductor element that allows capacitance to change according to the writing pressure like one disclosed in Japanese Patent Laid-Open No. 2013-161307. Furthermore, the writing pressure detecting unit may be configured by using a structure or an element that allows not capacitance but an inductance value or a resistance value to change according to the writing pressure. 
     It is to be noted that the embodiment of the present disclosure is not limited to the foregoing embodiments, and that various changes can be made without departing from the spirit of the present disclosure.