Patent Publication Number: US-2017349057-A1

Title: Communication terminal, communication terminal with electrode, communication system, electrically driven vehicle, and charging apparatus

Description:
TECHNICAL FIELD 
     The present invention generally relates to a communication terminal, an electrode-attached communication terminal, a communication system, an electric vehicle, and a charging apparatus, and more particularly to a communication terminal, an electrode-attached communication terminal, a communication system, an electric vehicle, and a charging apparatus used for communication between an electric device and a supply apparatus. 
     BACKGROUND ART 
     PTL 1 discloses a conventional power line connection device control system that allows automatic recognition of a type of electric device connected to each connection port (outlet) of a connection device. A power line carrier signal transmit-receive system is applied to the system described in PTL 1. A home server (control apparatus) is connected to a power line via a power line communication (PLC) modem. In this system, when an electric device that complies with the standard for power line carrier signal transmit-receive system is connected to the plug socket, the electric device exchanges signals with the home server via the power line and the PLC modem, and then a recognition process is performed. 
     However, since this system requires wiring work to connect the PLC modem directly to the power line, it is difficult to provide a communication function to an existing device later. When a power line to which relatively high voltage (for example, AC 200 V) is applied is used, the PLC modem may require relatively high-withstand-voltage components. 
     Meanwhile, PTL 2 discloses, for example, application of short-range wireless that uses an electromagnetic wave for communication between an electric device, such as an electric-powered vehicle and a supply apparatus (a charging stand) that supplies electric power to the electric device. In the supply apparatus described in PTL 2, the communication with the electric device (e.g., electric vehicle) is used, for example, for a billing process according to an amount of charging or the like. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laid-Open Publication No. 2003-110471 
     PTL 2: Japanese Utility Model No. 3148265 
     SUMMARY 
     A communication terminal includes a communication unit and a controller. The communication unit is provided in a supply apparatus that supplies electric power from a power source to an electric device through a feeding line, and is configured to communicate with a destination terminal provided in the electric device. The controller is configured to control a switch to switch turning on and off of the switch electrically connected to the feeding line. The feeding line includes a first line that electrically connects between the power source and the switch, and a second line that electrically connects between the switch and the electric device. At least one of the communication unit and the destination terminal is located away via a space from a conductive member included in the feeding line as to be electrically connected to an electrode coupled via electric field to the conductive member. The communication unit is configured to communicate with the destination terminal by using a signal transmitted via a conductive member included in the second line of the conductive member as a medium. The controller is configured to turn off the switch for a communication period for which the communication unit communicates with the destination terminal. 
     The communication terminal can perform one-to-one communication even when the supply apparatus and the electric device exist within a short distance under a one-to-plural or plural-to-one relationship. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic block diagram of a communication system according to Exemplary Embodiment 1. 
         FIG. 2  is a configuration diagram of a charging system that uses the communication system according to Embodiment 1. 
         FIG. 3  is a perspective view of a main part of an example of an installed first communication terminal according to Embodiment 1. 
         FIG. 4A  is a perspective view of a main part of an electrode according to Embodiment 1for illustrating an installing process thereof. 
         FIG. 4B  is a perspective view of the main part an installed electrode according to Embodiment 1. 
         FIG. 4C  is a perspective view of a charging cable which is a supply line according to Embodiment 1. 
         FIG. 4D  is a perspective view of a main part of another example of the installed first communication terminal according to Embodiment 1. 
         FIG. 5A  is a perspective view of a main part of the electrode according to Embodiment 1for illustrating an installation process thereof. 
         FIG. 5B  is a perspective view of the main part the installed electrode according to Embodiment 1. 
         FIG. 6A  is a cross-sectional view of a main part of an example of the electrode according to Embodiment 1. 
         FIG. 6B  is an enlarged sectional view of a main part of the electrode illustrated in  FIG. 6A . 
         FIG. 7A  is a perspective view of a main part of a ground terminal according to Embodiment 1 for illustrating a process for connecting the ground terminal. 
         FIG. 7B  is a perspective view of the main part of the ground terminal according to Embodiment 1 for illustrating a connection of the ground terminal. 
         FIG. 8A  is a perspective view of a main part of an example of an installed second communication terminal according to Exemplary Embodiment 1. 
         FIG. 8B  is a perspective view of a main part of an example of an installed second communication terminal according to Exemplary Embodiment 1. 
         FIG. 9  is a schematic block diagram of a supply apparatus according to Embodiment 1. 
         FIG. 10  is a schematic block diagram of the communication system according to Embodiment 1 for illustrating an operation of the communication system. 
         FIG. 11  is a perspective view of a main part of an installed first communication terminal according to Exemplary Embodiment 2. 
         FIG. 12  is a perspective view of a main part of an example of an installed first communication terminal according to Exemplary Embodiment 3. 
         FIG. 13  is a plan view of an electric vehicle and a charging apparatus that use a communication system according to a fifth exemplary embodiment. 
         FIG. 14  is a schematic block diagram of a communication system according to a sixth exemplary embodiment. 
     
    
    
     DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS 
     Exemplary Embodiment 1 
     In the following exemplary embodiments, a communication terminal, electrode-attached communication terminal, communication system, electric vehicle, and charging apparatus which are used for a charging system of an electric vehicle equipped with a secondary battery as one example will be described. An outline of the charging system will be described below. 
     &lt;Outline of Charging System&gt; 
       FIG. 1  is a schematic block diagram of a communication system according to Exemplary Embodiment 1.  FIG. 2  is a schematic diagram of charging system  10  that uses the communication system according to 
     Embodiment 1. Charging system  10  includes electric vehicle  1  and charging apparatus  2 , as illustrated in  FIG. 2 . 
     In accordance with the present embodiment, charging apparatus  2  charges secondary battery  11  installed to electric vehicle  1  (shown in  FIG. 1 ) by supplying, to electric vehicle  1 , electric power supplied from commercial power source (system power source) or a power generating facility, such as a photovoltaic power generating facility. That is, charging apparatus  2  supplies, to electric vehicle  1 , electric power supplied from power supply  8  (commercial power source or a power generating facility) via feeding line  7 . While the electric power to be supplied to charging apparatus  2  from the commercial power source or power generating facility may be either one of alternating current power and direct current power, the following describes a case of alternating current power as an example. The electric power to be supplied from charging apparatus  2  to electric vehicle  1  may also be either one of alternating current power and direct current power. The following describes a case of alternating current power as an example. 
     According to the embodiment, charging apparatus  2  is, for example, a charging stand installed on a ground in a parking lot of a commercial establishment, a public facility, or a collective housing. Charging apparatus  2  includes charging plug socket  21  (outlet) to which charging cable  5  is to be electrically connected. Charging plug socket  21  is configured to allow plug  51  of charging cable  5  to be detachably connected thereto. Charging plug socket  21  is electrically connected to feeding circuit  23  accommodated in housing  22  of charging apparatus  2  (shown in  FIG. 1 ). Accordingly, while charging cable  5  is connected to charging plug socket  21 , charging apparatus  2  supplies electric power from feeding circuit  23  via charging cable  5  to electric vehicle  1 . 
     Charging apparatus  2  includes lid  25  provided in front of charging plug socket  21  in housing  22 . Lid  25  is configured to be opened and closed. While lid  25  is opened, charging plug socket  21  is exposed. While lid  25  is closed, charging plug socket  21  is covered with lid  25 . Lid  25  is normally closed. When charging apparatus  2  is used, lid  25  is opened and plug  51  of charging cable  5  is plugged into and unplugged from charging plug socket  21 . That is, in order to connect charging cable  5  to charging plug socket  21 , a user opens lid  25  and plugs plug  51  into charging plug socket  21 , and then closes lid  25 . In order to disconnect charging cable  5  from charging plug socket  21 , the user opens lid  25  and unplugs plug  51  from charging plug socket  21 , and then closes lid  25 . A space large enough to accommodate plug  51  is provided between lid  25  and charging plug socket  21  so that lid  25  is closed while charging cable  5  is connected to charging plug socket  21 . 
     Charging apparatus  2  includes switch  231  (see  FIG. 1 ) electrically connected to feeding line  7 . Switch  231  is provided in feeding circuit  23 . Switch  231  is inserted into feeding line  7  that connects power source  8  to electric vehicle  1 . Conduction and non-conduction between power source  8  and electric vehicle  1  are switched along with switching of turning on and off of switch  231 . That is, while charging apparatus  2  is connected to electric vehicle  1  via charging cable  5 , when switch  231  is turned on (closed), power source  8  is electrically connected to electric vehicle  1  via feeding line  7 , and electric power is supplied from power source  8  to electric vehicle  1 . While charging apparatus  2  is connected to electric vehicle  1  via charging cable  5 , when switch  231  is turned off (opened), power source  8  is electrically disconnected from electric vehicle  1 , and electric power supply from power source  8  to electric vehicle  1  is stopped. Switch  231  is, for example, an electromagnetic relay, and is configured to be turned on and off in accordance with a control signal input from a controller of a communication terminal to be detailed later. 
     Feeding line  7  includes first line  71  (see  FIG. 1 ) that electrically connects power source  8  to switch  231 , and second line  72  (see  FIG. 1 ) that electrically connects switch  231  to electric vehicle  1 . That is, feeding line  7  is divided into first line  71  and second line  72  with switch  231  as a boundary between lines  71  and  72 . A portion of the feeding line  7  on the side of power source  8  from switch  231  is first line  71  while a portion of the feeding line  7  on the side of electric vehicle  1  from switch  231  is second line  72 . First line  71  is electrically connected to second line  72  when switch  231  is turned on. First line  71  is electrically disconnected from second line  72  when switch  231  is turned off. Charging cable  5  that connects charging apparatus  2  to electric vehicle  1  is included in second line  72  of feeding line  7 . Feeding circuit  23  may include, for example, a measurement circuit for measuring an amount of electric power supplied to electric vehicle  1 , and a voltage conversion circuit for performing voltage conversion, in addition to switch  231 . 
     Electric vehicle  1  has secondary battery  11  installed thereto. Battery  11  is charged with charging apparatus  2 . Electric vehicle  1  runs using electric energy stored in secondary battery  11 . While the following describes an electric-powered vehicle (EV) that runs using output of a motor as an example of electric vehicle  1 , electric vehicle  1  is not limited to the electric-powered vehicle. Electric vehicle  1  may be, for example, a plug-in hybrid vehicle (PHEV) that runs by combining engine output and motor output, a two-wheel vehicle (an electric motorcycle), a tricycle, or a power-assisted bicycle. 
     Electric vehicle  1  includes charging inlet  12  to which connector  52  of charging cable  5  is to be electrically connected. Charging inlet  12  is configured to allow connector  52  of charging cable  5  to be detachably connected thereto. Charging inlet  12  is electrically connected to charging circuit  14  (refer to  FIG. 1 ) accommodated in car body  13  of electric vehicle  1 . Accordingly, while charging cable  5  is connected to charging inlet  12 , electric vehicle  1  receives electric power from charging apparatus  2  via charging cable  5 , and charges secondary battery  11  by charging circuit  14 . 
     Charging system  10  may have any configuration to exchange electric power (electric energy) between charging apparatus  2  and electric vehicle  1 , and charging system  10  is not limited to the configuration to perform only charging of secondary battery  11 . That is, charging system  10  may be configured to discharge secondary battery  11 . In this case, charging system  10  can perform V2G (Vehicle to Grid), for example, by supplying electric power of secondary battery  11  from charging apparatus  2  to a distribution network. 
     In charging system  10  described above, an authentication process of electric vehicle  1  may be performed, for example, in order to perform billing according to an amount of charging, or in order to determine whether electric vehicle  1  is a vehicle to which charging is permitted or not. These applications require a communication between electric vehicle  1  and charging apparatus  2 . Therefore, in accordance with the following embodiments, the communication terminal, electrode-attached communication terminal, and communication system which are used for the communication between electric vehicle  1 , which is an electronic device, and charging apparatus  2 , which is a supplying apparatus, in charging system  10  will be described. 
     Although the configuration of the electrode-attached communication terminal as first communication terminal  3  as an example in accordance with the present embodiment will be described, an electrode-attached communication terminal with a configuration common to the configuration of first communication terminal  3  is also used as second communication terminal  4 . Therefore, unless otherwise specified, the following describes the electrode-attached communication terminal as first communication terminal  3  (also referred to as “electrode-attached communication terminal  3 ”), and the description of the electrode-attached communication terminal as second communication terminal  4  (also referred to as “electrode-attached communication terminal  4 ”) is omitted. 
     As illustrated in  FIG. 1 , electrode-attached communication terminal  3  according to the present embodiment includes communication unit  31 , electrode  32 , and ground terminal  35 . 
     Communication unit  31  is provided in the electric device (electric vehicle  1 ), and is configured to communicate with a destination terminal (second communication terminal  4 ). The destination terminal is provided in the supply apparatus that supplies electric power from power source  8  to electric device through feeding line  7 . Electrode  32  is configured to be located away via a space from conductive member  60  included in feeding line  7 , so as to be coupled via electric field to conductive member  60 . Here, conductive member  60  coupled via electric field to electrode  32  includes at least one of first conductor  601  included in charging cable  5 , and second conductor  602  electrically connected to first conductor  601 . Ground terminal  35  functions as a reference potential point of communication unit  31 . 
     Communication unit  31  is electrically connected to electrode  32  and ground terminal  35 , and is configured to communicate with the destination terminal by using a signal transmitted via conductive member  60  included in second line  72  of conductive member  60  as a medium. Ground terminal  35  is electrically connected to conductive part  131  of the electric device (electric vehicle  1 ). Conductive part  131  is made of conductive material. 
     In electrode-attached communication terminal  3 , electrode  32  is electrically coupled to conductive member  60  while not contacting conductive member  60  by being coupled via electric field to conductive member  60 . A signal is exchanged with the destination terminal via by using conductive member  60  as a medium to allow electrode-attached communication terminal  3  to perform electric field communication with the destination terminal. The electric field communication is a communication in which a predetermined signal propagates through a particular communication path (conductive member  60 ) mainly by using a static electrostatic field or a quasi-electrostatic field. For example, the electric field communication is communication that transmits a predetermined signal by using an electric field that occurs between conductive member  60  and the ground. Components of an electric field (static electrostatic field or quasi-electrostatic field) at a position attenuate in proportion to the third power of the distance from the position to electrode  32  when propagating through space. That is, the electric field used by the electric field communication mentioned here rapidly attenuates depends on the distance from electrode  32 . Unlike radiated waves of wireless communication, the signal transmitted by this electric field communication does not propagate through a space with little attenuation. This electric field communication establishes communication between terminals connected through a particular communication path instead of an unspecified path in space. Also, in the electric field communication mentioned here, since attenuation of the electric field while propagating through conductive member  60  is smaller than a case of propagating through space, communication can be established with very small energy although non-contact, compared with wireless communication using radiated waves. 
     In the above configuration, in electrode-attached communication terminal  3 , ground terminal  35  constituting the reference potential point of communication unit  31  is electrically connected to conductive part  131 . Conductive part  131  mentioned here is a portion with conductivity, and may be a metal portion that is substantially equipotential in car body  13  (see  FIG. 2 ) including a frame and body. In general, conductive part  131  is electrically connected to a negative terminal of a battery for electric parts (different from secondary battery  11  for driving). In other words, ground terminal  35  connected to conductive part  131  grounds communication unit  31  to the body. This configuration reduces impedance of the reference potential point of communication unit  31  more than a case where ground terminal  35  is not electrically connected to conductive part  131  (electrically isolated), thus stabilizing a potential of the reference potential point. 
     In more detail, in a case where electrode-attached communication terminal  3  communicates with the destination terminal, when communication unit  31  applies a signal to electrode  32 , an electric field occurs between conductive member  60  and the ground, for example, as described above. At this moment, if ground terminal  35  is not connected to conductive part  131 , both conductive part  131  that exists near electrode  32  and the ground can be end points of electric force lines that start from electrode  32 , hence preventing the electric field from being unstable. For example, one electric force line flows along a path extends from electrode  32  as a starting point to conductive part  131  as an end point and further extends from conductive part  131  as a starting point to the ground as an end point. Another electric force line flows along a path that extends from electrode  32  directly to the ground. Thus, various electric fields (paths of electric force line) exist, and the signal used in the above-described electric field communication is likely to be affected by an installation position of electrode-attached communication terminal  3  and conductive part  131  around electrode-attached communication terminal  3 . Such unstable electric field may cause variations in a signal transmission efficiency and reduction in the signal. Meanwhile, when ground terminal  35 , which is the reference potential point of communication unit  31 , is connected to conductive part  131 , the end points of the electric force lines that start from electrode  32  is converged on conductive part  131 . This provides stable electric field used for the electric field communication and improves the signal transmission efficiency. 
     Conductive member  60  is preferably made of metal. Although communication can be established even if conductive member  60  is made of conductive resin, such as, conductive polymer since metal generally has higher conductivity than conductive resin, conductive member  60  made of metal can reduce a loss in the communication path. Also, for example, although communication can be established even if a medium that is mainly made of water is used as conductive member  60 , such as a human body, water hose, and piping for water, this medium can lead to large loss in the communication path in a similar manner to the conductive resin. Furthermore, such a medium mainly made of water does not have a stable shape, and for example, substantial electrical conductivity of a human body will change depending on posture thereof or the like. Therefore, conductive member  60  made of metal is more preferable to communication stability. 
     In the present exemplary embodiment, as an example, the electric device is electric vehicle  1 . The supply apparatus is charging apparatus  2 . Feeding line  7  includes charging cable  5  that connects electric vehicle  1  to charging apparatus  2 . In the present exemplary embodiment, for first communication terminal  3  provided in electric vehicle  1 , second communication terminal  4  is the destination terminal, and first communication terminal  3  communicates with second communication terminal  4 . In contrast, for second communication terminal  4  provided in charging apparatus  2 , first communication terminal  3  is the destination terminal, and second communication terminal  4  communicates with first communication terminal  3 . 
     The electrode-attached communication terminal according to the present exemplary embodiment will be detailed below. However, the configuration to be described below is only one example of the present invention, the present invention is not limited to the following exemplary embodiment, and various changes according to design or the like can be made, even other than this exemplary embodiment, without departing from technical ideas according to the present invention. 
     &lt;Configuration of Electrode-Attached Communication Terminal&gt; 
       FIG. 3  is a perspective view of a, main part of installed first communication terminal  3  according to Embodiment 1.  FIG. 4A  and  FIG. 4B  are perspective views of main parts of electrode  32  for illustrating an installation process thereof. In addition to communication unit  31 , electrode  32 , and ground terminal  35  described above, electrode-attached communication terminal  3  according to the present embodiment further includes controller  313 , power supply circuit  314 , case  33  (refer to  FIG. 3 ), cable  34  that connects communication unit  31  to electrode  32 , and cable  36 . Case  33  accommodates therein communication unit  31 , controller  313 , and power supply circuit  314 . Cable  36  connects communication unit  31  to ground terminal  35 . 
     Electrode  32  is electrically connected to communication unit  31  via cable  34 . Since electrode-attached communication terminal  3  according to the present exemplary embodiment performs electric field communication while electrode  32  is electrically coupled to conductive member  60  while not contacting conductive member  60 , electrode  32  is used while not directly contacting conductive member  60 . 
       FIG. 4C  is a perspective view of charging cable  5  which is the supply line in accordance with Embodiment 1. First conductor  601  included in the supply line includes core wire  534  (see  FIG. 4 ) of electric wire  53  (see  FIG. 4 ) included in charging cable  5 . Second conductor  602  electrically connected to first conductor  601  includes core wire  154  (refer to  FIG. 4A ) of internal wire  15  (refer to  FIG. 3 ) that electrically connect charging inlet  12  and charging circuit  14  in the electronic device (electric vehicle  1 ). Each of these electric wires (electric wire  53  and internal wire  15 ) is, for example, a vinyl insulated wire in which a copper core wire is covered with a sheath made of, e.g. vinyl. Electrode  32  is located away via a space from conductive member  60  including at least one of first conductor  601  and second conductor  602  as described above, thereby being coupled via electric field to conductive member  60 . In accordance with the present embodiment, conductive member  60  includes second conductor  602  while electrode  32  is coupled via electric field to second conductor  602 . 
     Here, in accordance with the present embodiment, electrode  32  is configured to be coupled via electric field to conductive member  60  by being capacitively coupled to conductive member  60 . Here, a capacitance component formed between electrode  32  and conductive member  60  (hereinafter referred to as “coupling capacitance”) is determined by a distance from electrode  32  to conductive member  60  and a dielectric constant of a substance that lies between electrode  32  and conductive member  60 . A space large enough to form a coupling capacitance may be provided between electrode  32  and conductive member  60 . It is not essential that sheath  155  lies between electrode  32  and conductive member  60 , and that, for example, a gap (space) may exist between electrode  32  and conductive member  60 . 
     Electrode  32  coupled via electric field to conductive member  60  by capacitive coupling can reduce a coupling loss between electrode  32  and conductive member  60 . Although electric field coupling between electrode  32  and conductive member  60  can also be performed, for example, by disposing electrode  32  including a wire to be entwined conductive member  60 , such electric field coupling causes a larger coupling loss than capacitive coupling. In capacitive coupling, since electrode  32  faces a surface of conductive member  60  in parallel, the coupling loss between electrode  32  and conductive member  60  can be reduced. 
     As detailed later, electrode  32  is preferably made of a conductive sheet. For example, electrode  32  is more preferably made of, e.g. a mesh metal sheet, a metal foil, or a metal tape. 
     Communication unit  31  includes transmitting circuit  311  and receiving circuit  312 , as illustrated in  FIG. 1 . 
     Transmitting circuit  311  is electrically connected to electrode  32 , and is configured to generate a transmission signal that contains information by modulating a carrier wave (carrier) and to apply the transmission signal to electrode  32 . Transmitting circuit  311  uses, for example, a rectangular wave having a frequency of about 10 [MHz] as the carrier wave, and employs On Off Keying (OOK) as a modulation method. When transmitting circuit  311  applies the transmission signal to electrode  32 , an electric field (quasi-electrostatic field) is induced in conductive member  60  coupled via electric field to electrode  32 . The electric field induced in conductive member  60  propagates through conductive member  60  with a little attenuation, and then, reaches the supply device (charging apparatus  2 ). Receiving circuit  412  of the destination terminal (second communication terminal  4 ) provided in the supply device thus receives the transmission signal. 
     Receiving circuit  312  is electrically connected to electrode  32 , and is configured to receive the transmission signal from the destination terminal. 
     Receiving circuit  312  receives the transmission signal induced in electrode  32  by the electric field generated in conductive member  60  coupled via electric field to electrode  32 . Then, receiving circuit  312  demodulates the transmission signal to extract information contained in the transmission signal. 
     Controller  313  mainly includes a micro processing unit (MPU) configured to control transmitting circuit  311  and receiving circuit  312 . This configuration enables communication unit  31  to communicate with the destination terminal (second communication terminal  4 ) by using the signal transmitted via conductive member  60  as a medium. Communication unit  31  including both transmitting circuit  311  and receiving circuit  312  can exchange the transmission signal, and can perform bidirectional communication with the destination terminal. 
     Power supply circuit  314  is configured to supply electric power for operations to transmitting circuit  311 , receiving circuit  312 , and controller  313 . Power supply circuit  314  includes, for example, a primary battery as a power supply, and supplies electric power of the primary battery to the circuits. 
     Ground terminal  35  is electrically connected to communication unit  31  via cable  36 . Ground terminal  35  is electrically connected to each of transmitting circuit  311 , receiving circuit  312 , controller  313 , and power supply circuit  314 , and functions as a reference potential point of each circuit. That is, for power supply circuit  314 , for example, since ground terminal  35  is electrically connected to an output terminal on a lower (negative) potential side, power supply circuit  314  outputs a voltage corresponding to a potential difference between an output terminal on a higher (positive) potential side and ground terminal  35  as a power source voltage. 
     As detailed later, ground terminal  35  preferably has a structure, such as a spade terminal, suitable for being grounded to the body. That is, ground terminal  35  is electrically connected to conductive part  131  made of a conductive material out of car body  13  of electric vehicle  1 , and thus ground terminal  35  preferably has a structure suitable to be electrically connected to conductive part  131 . 
     Communication unit  31  is configured to communicate with the destination terminal while the electronic device is connected to the supply apparatus via feeding line  7 . Communication unit  31  is configured not to communicate with the destination terminal while the electronic device is connected to the supply apparatus via the feeding line. In accordance with the embodiment, as described above, the electronic device is electric vehicle  1 , the supply apparatus is charging apparatus  2 , and feeding line  7  includes charging cable  5 . Second communication terminal  4  is the destination terminal for first communication terminal  3  provided in electric vehicle  1 . 
     Therefore, communication unit  31  of first communication terminal  3  communicates with second communication terminal  4  while electric vehicle  1  is connected to charging apparatus  2  via charging cable  5 . Communication unit  31  does not communicate with second communication terminal  4  while electric vehicle  1  is not connected to charging apparatus  2  via charging cable  5 . It is determined whether or not electric vehicle  1  is connected to charging apparatus  2  via charging cable  5 , based on a detection result of a connection detector that detects a connection status of plug  51  of charging cable  5  to charging plug socket  21 . 
     When the connection detector detects that plug  51  is connected to charging plug socket  21 , communication unit  31  determines that the electronic device is connected to the supply apparatus via feeding line  7 , and then, communication unit  31  communicates with second communication terminal  4  which is the destination terminal. On the other hand, when the connection detector detects that the connection between plug  51  and charging plug socket  21  is canceled, communication unit  31  determines that the electronic device is not connected to the supply apparatus via feeding line  7 , and then, does not communicate with second communication terminal  4  which is the destination terminal. The connection detector may be included in communication unit  31 , but may be provided separately from communication unit  31 . The connection detector is configured to detect the connection status of plug  51  of charging cable  5  to charging plug socket  21  optically, for example, by using reflection of infrared light or the like, or to detect the connection status electrically based on an electric power application state. Instead of the connection status of plug  51  to charging plug socket  21 , the connection detector may detect the connection status of connector  52  of charging cable  5  to charging inlet  12 . 
     That is, first communication terminal  3  and second communication terminal  4  mainly use an electric field component that attenuates in proportion to the third power of a distance from electrode  32  when propagating through space, and performs communication by electric field communication by which a predetermined signal propagates through a particular communication path (conductive member  60 ). Accordingly, even when electric vehicle  1  is not connected to charging apparatus  2  via charging cable  5 , first communication terminal  3  and second communication terminal  4  can be in a communicative status, e.g. when plug  51  of charging cable  5  exists near charging plug socket  21 . By communicating with the destination terminal only when the electronic device is connected to the supply apparatus via feeding line  7  as described above, communication unit  31  can communicate only when being connected via a wire similarly to a wired communication although non-contact. 
     The connection detector that determines whether or not electric vehicle  1  is connected to charging apparatus  2  via charging cable  5  is not essential. The communication system according to the present embodiment functions when the electric device is connected to the supply apparatus via feeding line  7  and first communication terminal  3  and second communication terminal  4  can communicate with each other. For example, when second communication terminal  4  receives a signal transmitted from first communication terminal  3 , the communication path for electric field communication is not established before electric vehicle  1  is connected to charging apparatus  2  (via charging cable  5 ). Accordingly, the signal from first communication terminal  3  propagates through space before reaching second communication terminal  4 , and a signal strength received at second communication terminal  4  is very small. When electric vehicle  1  is connected to charging apparatus  2  (via charging cable  5 ) in this state, the communication path for electric field communication is established, and the signal strength received at second communication terminal  4  increases rapidly. A receiving strength difference is, for example, ranges from 40 [dB] to 70 [dB] between before and after electric vehicle  1  is connected to charging apparatus  2  via charging cable  5  although it depends on the distance between electric vehicle  1  and charging apparatus  2 , the size of electric vehicle  1 , and the length of charging cable  5 . This value of the reception strength difference is one example when the distance between electric vehicle  1  and charging apparatus  2  is about 1 [m] and overall length of electric vehicle  1  is about 2 [m] to 5 [m]. That is, by setting receiving sensitivity of the communication terminal on a signal receiving side in accordance with this value of the signal reception strength difference, first communication terminal  3  and second communication terminal  4  can communicate with each other only when electric vehicle  1  is connected to charging apparatus  2  via charging cable  5 . In other words, through setting of the receiving sensitivity, communication unit  31  is configured to communicate with the destination terminal while the electric device is connected to the supply apparatus via feeding line  7 , and not to communicate with the destination terminal while the electric device is not connected to the supply apparatus via feeding line  7 . 
     Even while plug  51  of charging cable  5  is located immediately close to charging plug socket  21 , the receiving strength difference is equal to or greater than 20 [dB] when compared with a case where electric vehicle  1  is connected to charging apparatus  2  via charging cable  5 . The receiving sensitivity is set in accordance with the difference, and thereby, first communication terminal  3  and second communication terminal  4  can determine whether or not electric vehicle  1  is connected to charging apparatus  2  via charging cable  5  with establishment of communication. Therefore, the connection detector for determining whether or not electric vehicle  1  is connected to charging apparatus  2  via charging cable  5  is not essential. 
     &lt;Configuration of Communication Terminal&gt; 
     Communication unit  31  of electrode-attached communication terminal  3  with the above described configuration, together with controller  313  and power supply circuit  314 , constitutes communication terminal  30  including neither electrode  32  nor ground terminal  35 . That is, communication terminal  30  according to the present embodiment includes communication unit  31  and controller  313 . Communication terminal  30  includes feeding connection terminal  315  electrically connected to electrode  32 . Communication terminal  30  further includes ground connection terminal  316  electrically connected to ground terminal  35 . 
     Connector  341  provided at an end of cable  34  opposite to electrode  32  is detachably connected to feeding connection terminal  315 . That is, while connector  341  is connected to feeding connection terminal  315 , feeding connection terminal  315  is electrically connected to electrode  32  via cable  34 . Feeding connection terminal  315  is disposed to be exposed from a part of case  33 . 
     Connector  361  provided at an end of cable  36  opposite to ground terminal  35  is detachably connected to ground connection terminal  316 . That is, while connector  361  is connected to ground connection terminal  316 , ground connection terminal  316  is electrically connected to ground terminal  35  via cable  36 . Ground terminal  35  is disposed to be exposed from a part of case  33 . 
     Communication terminal  30  thus configured, together with electrode  32  and ground terminal  35 , constitutes electrode-attached communication terminal  3  described above by connecting electrode  32  to feeding connection terminal  315  and connecting ground terminal  35  to ground connection terminal  316 . Therefore, when plural types of electrodes  32  exist, communication terminal  30  can connect and use arbitrary electrode  32  out of plural types of electrodes  32 . When plural types of ground terminals  35  exist, communication terminal  30  can connect and use arbitrary ground terminal  35  out of plural types of ground terminals  35 . 
     &lt;Configuration of Electrode&gt; 
     A configuration of electrode  32  will be described below. 
     In accordance with the embodiment, electrode  32  is a conductive sheet. Since electrode  32  is made of conductive material, electrode  32  can, for example, efficiently convert the transmission signal (electric power) output from transmitting circuit  311  into an electric field, and superimpose the converted transmission signal on first conductor  601  or second conductor  602  as the electric field. This is because the entire of electrode  32  made of conductive material is generally equipotential to generate almost no electric loss, allowing the transmission signal to be applied onto the entire of electrode  32  substantially uniformly without a loss. This configuration reduces a loss of the transmission signal in a communication path, such as a path from transmitting circuit  311  to receiving circuit  412  of the destination terminal (second communication terminal  4 ). Communication unit  31  can thus reduce electric power necessary for communication. In particular, when communication unit  31  is power by a battery, this configuration prolongs the battery life and the battery replacement cycle. 
     Electrode  32  may be made of non-conductive material (electrically insulating material), such as synthetic resin. Even in this case, electrode  32  can be coupled via electric field to conductive member  60 . However, in electrode  32  made of electrically insulating material, a potential on a surface of electrode  32  becomes non-uniform, and the electric loss on the surface of electrode  32  is larger than electrode  32  made of conductive material, which may cause a larger transmission loss. 
     Electrode  32  is coupled via electric field to second conductor  602  by being wound around internal wire  15 , as illustrated in  FIG. 3 . Electrode  32  is wound around internal wire  15  on sheath  155  (refer to  FIG. 4A ). 
     In other words, with respect to internal wire  15  having the structure in which second conductor  602  composed of core wire  154  is covered with sheath  155 , electrode  32  is disposed as to face second conductor  602  across sheath  155  without breaking sheath  155 . Therefore, a distance from electrode  32  to second conductor  602  is generally identical to the thickness of sheath  155 . Thus, electrode  32  which is located away via a space of the thickness of sheath  155  from conductive member  60  (second conductor  602 ), is capacitively coupled (electric field coupling) to conductive member  60 . 
     In accordance with the embodiment, electrode  32  surrounds conductive member  60  in an entire circumference of a circumferential direction of conductive member  60 . That is, in the case that conductive member  60  (second conductor  602 ) is composed of core wire  154  of internal wire  15 , electrode  32  surrounds conductive member  60  in the entire circumference of the circumferential direction in a cross-section perpendicular to an extending direction (lengthwise direction) of internal wire  15 . This configuration ensures the facing area of electrode  32  facing conductive member  60  as large as possible, and reduces the transmission loss. That is, when the facing area of electrode  32  facing conductive member  60  increases, a coupling capacitance between electrode  32  and conductive member  60  increases, accordingly decreasing the transmission loss. Note that methods for reducing the transmission loss (coupling loss) in a coupling section between electrode  32  and conductive member  60  include a method for matching impedance in addition to the above-described method. For example, impedance of communication terminal  30  (communication unit  31 ) from electrode  32  is determined to be matched with impedance of electrode  32  from communication terminal  30  at a frequency of the carrier wave of the transmission signal, thereby decreasing the coupling loss. As in the present exemplary embodiment, in the case where the frequency of the carrier wave is about 10 [MHz], when the impedance of communication terminal  30  from electrode  32  is similar to the impedance of electrode  32  from communication terminal  30  at about 10 [MHz], which is the frequency of the carrier wave, the coupling loss can be reduced. 
     Electrode  32  may not necessarily surround conductive member  60  in the entire circumference of the circumferential direction of conductive member  60 . Electrode  32  may surround conductive member  60  except for a part of conductive member  60  in the circumferential direction of conductive member  60 . Even in the case where there is no space around internal wire  15  to wind electrode  32  in the entire circumference of the circumferential direction of internal wire  15 , electrode  32  can be coupled via electric field to conductive member  60 . 
     In accordance with the embodiment, it is assumed that a wiring between charging apparatus  2  and electric vehicle  1  is single-phase three-wire system 100V wiring. That is, as illustrated in  FIG. 3  and  FIG. 4D , internal wire  15  as conductive member  60  includes neutral line  153  of N phase and a pair of voltage lines  151  and  152  of L1 phase and L2 phase. Neutral line  153  is electrically connected, for example, to a stable potential point, such as the ground, via charging cable  5  of charging apparatus  2 . 
     That is, neutral line  153  is grounded. This configuration causes a voltage of neutral line  153  with respect to the ground to become 0 [V], and causes a voltage of each of the pair of voltage lines  151  and  152  with respect to the ground to become 100 [V]. The voltage between one voltage line  151  (L1 phase) and neutral line  153  (N phase) becomes 100 [V], the voltage between another voltage line  152  (L2 phase) and neutral line  153  (N phase) becomes 100 [V]. The voltage between the pair of voltage lines  151 ,  152  becomes 200 [V]. 
     That is, conductive member  60  includes neutral line  153  and voltage lines  151  and  152 . Electrode  32  is configured to be coupled via electric field only to voltage lines  151  and  152  out of neutral line  153  and voltage lines  151  and  152 . In the configuration shown in  FIG. 3 , as the pair of voltage lines  151  and  152  is bundled with electrode  32 , electrode  32  is wound around two of three internal wires  15  (both voltage lines  151  and  152 ). On the other hand, in the example shown in  FIG. 4D , electrode  32  is wound only around one voltage line  151  out of the pair of voltage lines  151  and  152 . In the example shown in  FIG. 4D , electrode  32  is wound so as to closely adhere to sheath  155  with almost no gap. 
     Thus, electrode  32  is preferably coupled via electric field only to voltage lines  151  and  152  excluding neutral line  153  of conductive member  60 . That is, in the electric field communication, since signals are transmitted using an electric field generated between conductive member  60  and a reference potential point, neutral line  153  which can be the reference potential point is preferably not included in conductive member  60 . Electrode  32  is coupled via electric field to both of the pair of voltage lines  151  and  152 , as illustrated in  FIG. 3 . 
       FIG. 4D  is a perspective view of a main part of another example of installed first communication terminal according to Embodiment 1. In  FIG. 4D , components identical to those of the first communication terminal illustrated in  FIG. 3  are denoted by the same reference numerals. Electrode  32  illustrated in  FIG. 4D  is coupled via electric field only to one of the pair of voltage lines  151  and  152 , and is not coupled via electric field to the other of the pair of voltage lines  151  and  152 . Comparing these configurations, the signal receiving strength is higher in the configuration shown in  FIG. 3  (electrode  32  is coupled via electric field to both of the pair of voltage lines  151  and  152 ) than in the configuration shown  FIG. 4D  (electrode  32  is coupled via electric field only to one of the pair of voltage lines  151  and  152 ). 
     In the examples shown in  FIG. 4A  and  FIG. 4B , electrode  32  is a mesh sheet having a strip shape, and is wound around internal wire  15  plural turns around internal wire  15 . In this configuration, electrode  32  preferably has a configuration in which an adhesive is coated on one surface in terms of workability. In this configuration, electrode  32  is relatively thin and easy to wind, and thus it is easy to wind electrode  32  around relatively thin (with a small diameter) internal wire  15  so as to cause electrode  32  to adhere securely thereto. 
       FIG. 5A  and  FIG. 5B  are perspective views of a main part of still another installment process of electrode  32  according to Embodiment 1. In the examples shown in  FIG. 5A  and  FIG. 5B , hook-and-loop fastener  321  is provided on both sides of electrode  32 . In this configuration, electrode  32  is wound around internal wire  15  and fixed with hook-and-loop fastener  321  on both sides of electrode  32  while being rolled around internal wire  15 . Since electrode  32  is detachable in this configuration, electrode-attached communication terminal  3  including electrode  32  can be easily removed from internal wire  15  at a time of, e.g. maintenance of electrode-attached communication terminal  3 . 
     Electrode  32  is preferably made of a mesh metal sheet, a metal foil, a metal tape, or the like as described above. This configuration allows electrode  32  to closely adhere to the surface of internal wire  15  easily, and reduces the transmission loss. In particular, the mesh metal sheet more preferably adheres to the surface of internal wire  15  than the metal foil or the metal tape. The mesh metal sheet can be wound around internal wire  15  with almost no air layer that lies between internal wire  15  and the metal sheet. In short, magnitude of a coupling capacitance between electrode  32  and conductive member  60  is determined by a distance from electrode  32  to conductive member  60  and a dielectric constant of the substance that lies between electrode  32  and conductive member  60 . The transmission loss decreases as the coupling capacitance increases. Therefore, electrode  32  securely adhering to internal wire  15  reduces the distance from electrode  32  to conductive member  60 , and prevents an air layer from lying between electrode  32  and conductive member  60 , thereby providing a large coupling capacitance and a small transmission loss. 
     In the case that electrode  32  has a mesh structure, internal wire  15  is exposed from meshes of electrode  32 , hence not being covered with electrode  32  completely. However, when a high-frequency transmission signal with the carrier wave having a frequency equal to or higher than several megahertz is used for communication, electrode  32  failing to cover internal wire  15  completely does not much affect the transmission loss. 
       FIG. 6A  is a cross-sectional view of a main part of another example of electrode  32  according to Embodiment 1.  FIG. 6B  is an enlarged sectional view of section  6 B of electrode  32  illustrated in  FIG. 6A . Electrode-attached communication terminal  3  may further include electrical insulator  322  that covers electrode  32  as illustrated in  FIG. 6A  and  FIG. 6B . In the examples shown in  FIG. 6A  and  FIG. 6B , electrical insulator  322  made of sheath material made of synthetic resin covers both sides of electrode  32 . Electrical insulator  322  is formed, for example, by coating electrode  32  with the resin or winding a tape with electrical insulation properties around electrode  32 . This structure prevents electrode  32  from directly contacting a metal conductor around internal wire  15 . Since electrode  32  is protected by electrical insulator  322 , even when electrode  32  is made of copper or other materials, aged deterioration of electrode  32  caused by rust or the like is inhibited, resulting in that low transmission loss can be maintained over long periods. For purposes of rust prevention of electrode  32 , electrical insulator  322  preferably has a water shielding property so as to prevent water from attaching to electrode  32 . Electrical insulator  322  may be provided only on one side of electrode  32 . In this case, electrode  32  is wound around internal wire  15  with a surface of electrode  32  facing electrical insulator  322  being outside, and electrode  32  is not exposed from electrical insulator  322 . 
     In the case that conductive member  60  has a linear shape or a tubular shape extending in extending direction D 32 , the length of electrode  32  in extending direction D 32  of conductive member  60  is preferably smaller than ¼ of a wavelength of the above-described signal. In the following, the length of electrode  32  in extending direction D 32  of conductive member  60  is referred to as coupling length Lc of electrode  32  (refer to  FIG. 3 ). That is, when the signal used in electrode-attached communication terminal  3  for communication has a wavelength λ [ml], coupling length Lc of electrode  32  is preferably less than λ/4 [m]. The signal wavelength X mentioned here is a wavelength of the carrier wave (carrier) of the transmission signal. For example, when transmitting circuit  311  transmits the signal (transmission signal) by using the carrier wave of 10 [MHz] as described above, the signal wavelength λ is 30 [m]. In this case, coupling length Lc of electrode  32  is preferably less than 7.5 [m] (=30/4 [m]). In this structure, electrode  32  is unlikely to function as an antenna for an electromagnetic wave of wavelength λ identical to the wavelength of the transmission signal, and electrode  32  is less susceptible to electromagnetic waves. 
     &lt;Configuration of Ground Terminal&gt; 
     A configuration of ground terminal  35  will be described below. 
       FIG. 7A  and  FIG. 7B  are perspective views of a main part of a process of connecting ground terminal  35  according to Embodiment 1. In the present embodiment, ground terminal  35  includes a spade terminal that can be fastened together with conductive part  131  with screw  132  (a male screw, such as a hexagon head bolt or a truss screw, or a female screw, such as a nut), as illustrated in  FIG. 7A . Ground terminal  35  is electrically connected to conductive part  131  with screw  132  tightly fastened originally to conductive part  131 . That is, during installation of ground terminal  35 , an operator first loosens appropriate screw  132  tightly fastened to conductive part  131 , as illustrated in  FIG. 7A , and then, inserts ground terminal  35  into a gap formed between screw  132  and conductive part  131 . In the example shown in  FIG. 7A , screw  132  (hexagon head bolt) that fixes metal plate  133  to frame  134  is used for installing ground terminal  35 . While being fixed to frame  134  with screw  132 , metal plate  133  is electrically connected to frame  134 . Metal plate  133  and frame  134  are included in conductive part  131 . 
     After inserting ground terminal  35  into the gap between screw  132  and conductive part  131 , the operator tightens screw  132  to tightly fasten ground terminal  35  together with metal plate  133  with screw  132 , as illustrated in  FIG. 7B . At this moment, ground terminal  35  is electrically connected to metal plate  133  and frame  134  which constitute conductive part  131 . Thus, ground terminal  35  is electrically connected to conductive part  131  and is grounded via a fastening portion of screw  132  in conductive part  131  as a grounding point. 
     Ground terminal  35  is connected to conductive part  131  without processing conductive part  131 . Screw  132  tightly fastened maintains a small contact resistance between ground terminal  35  and conductive part  131 . In particular, since ground terminal  35  is a spade terminal, ground terminal  35  can be connected only by loosening screw  132  without removing screw  132  completely, providing preferable workability. However, the spade terminal is just an example of ground terminal  35 , and ground terminal  35  may be a round terminal or any other terminal 
     Conductive part  131  to which ground terminal  35  is connected is a portion with conductivity, such as a metal portion that is substantially equipotential in car body  13  of electric vehicle  1  as described above. The surface area of conductive part  131  is preferably larger than the surface area of ground terminal  35 . Ground terminal  35  connected to conductive part  131  provides stable electric field used for electric field communication and further improvement in the signal transmission efficiency. That is, since the electric field does not occur within the conductor, ground terminal  35  as the reference potential point of communication unit  31  connected to conductive part  131  with a larger surface area stabilizes the electric field significantly. As a result, this configuration allows further improvement in the signal transmission efficiency. 
     The volume of conductive part  131  is preferably larger than the volume of ground terminal  35 . Ground terminal  35  connected to conductive part  131  provides stable electric field used for electric field communication and further improvement in the signal transmission efficiency. That is, since impedance of a conductor decreases as the thickness of the conductor increases, ground terminal  35  as the reference potential point of communication unit  31  connected to conductive part  131  with a larger volume provides small impedance of the reference potential point significantly. As a result, this configuration provides stable potential of the reference potential point easily, and further improves the signal transmission efficiency. 
     In accordance with the present embodiment, both of the surface area and volume of conductive part  131  is larger than both of the surface area and volume of ground terminal  35 , respectively. However, this configuration is not necessarily required, and one or both of the surface area and volume of conductive part  131  may be smaller than one or both of the surface area and volume of ground terminal  35 , respectively. 
     As another configuration example, ground terminal  35  may be a terminal that is connected to an already-installed ground wiring electrically connected to conductive part  131 . That is, when a ground wiring connected to conductive part  131  exists near a fixing position of communication unit  31  in car body  13 , ground terminal  35  is connected to this ground wiring, and is electrically connected to conductive part  131 . In this case, ground terminal  35  can be, for example, with a terminal such as a screw terminal connected to a distal end of the ground wiring, an electrotap that allows the ground wiring to branch through connection in an intermediate portion of the ground wiring. 
     As still another configuration example, ground terminal  35  may be electrically connected to case  33  of communication unit  31 . That is, in the case that case  33  is made of a conductive metal, ground terminal  35  may be electrically connected to conductive part  131  with ground terminal  35  being electrically connected to case  33  and case  33  being connected to conductive part  131 . In this case, case  33  or a metal stay for installing case  33  is fastened together to conductive part  131  with screw  132 , and thus ground terminal  35  is electrically connected to conductive part  131  via case  33 . 
     The resistance between an arbitrary portion in conductive part  131  and ground terminal  35  is preferably equal to or less than several hundred [ohms]. This configuration increases the above-described effect produced by electrical connection of ground terminal  35  to conductive part  131 . 
     &lt;Method for Installing Electrode-Attached Communication Terminal&gt; 
     When installing electrode-attached communication terminal  3 , an operator fixes communication unit  31  of electrode-attached communication terminal  3  to a predetermined position of electric vehicle  1  (electronic device), and causes electrode  32  to be coupled via electric field to conductive member  60 . At this moment, the operator can cause electrode  32  to be coupled via electric field to conductive member  60  by winding electrode  32  on sheath  155  around internal wire  15 . 
     The operator fixes communication unit  31  by fixing case  33  together with a bolt near charging inlet  12  in the car body of electric vehicle  1 . A fixing position where communication unit  31  is fixed to electric vehicle  1  is determined according to a length of cable  34  so as to allow cable  34  to connect communication unit  31  to electrode  32 . In the case that communication unit  31  includes a primary battery as a power source in power supply circuit  314 , the operator does not need to connect an external power source to communication unit  31  in order to secure electric power for operating communication unit  31 . 
     The operator electrically connects ground terminal  35  to conductive part  131 . At this moment, by fastening ground terminal  35  composed of a spade terminal with screw  132  together to conductive part  131  as described above, the operator can electrically connect ground terminal  35  to conductive part  131 . In the case that screw  132  is tightly fastened to conductive part  131  near the fixing position of communication unit  31  around charging inlet  12 , the operator preferably connects ground terminal  35  with screw  132 . 
     Thus, during installation of electrode-attached communication terminal  3  according to the present embodiment in electric vehicle  1 , the operator does not need to electrically connect electrode  32  of electrode-attached communication terminal  3  to an electric system of electric vehicle  1 , and can perform installation with relatively simple work without processing the electric system of electric vehicle  1 . Therefore, when electric vehicle  1  as the electric device has a space for installing electrode-attached communication terminal  3 , electrode-attached communication terminal  3  can be easily installed to electric vehicle  1  as the electric device by post-installation. The operation for connecting ground terminal  35  to conductive part  131  does not involve processing of electric system of the electric vehicle  1 , and thus, does not prevent post-installation of electrode-attached communication terminal  3 . 
     &lt;Configuration of Second Communication Terminal&gt; 
     In accordance with the embodiment, as described above, first communication terminal  3  provided in the electronic device has the same basic configuration as second communication terminal  4  provided in the supply apparatus. Therefore, the description of electrode-attached communication terminal  3  described above as first communication terminal  3  becomes the description of electrode-attached communication terminal  4  as second communication terminal  4  by interpreting the electronic device (electric vehicle  1 ) as the supply apparatus (charging apparatus  2 ). Here, communication terminal  30 , communication unit  31 , electrode  32 , case  33 , and cable  34  of first communication terminal  3  correspond to communication terminal  40 , communication unit  41 , electrode  42 , case  43 , and cable  44  of second communication terminal  4 , respectively. Ground terminal  35  and cable  36  of first communication terminal  3  corresponds to ground terminal  45  and cable  46  of second communication terminal  4 , respectively. Transmitting circuit  311 , receiving circuit  312 , controller  313 , power supply circuit  314 , feeding connection terminal  315 , and connector  341  correspond to transmitting circuit  411 , receiving circuit  412 , controller  413 , power supply circuit  414 , feeding connection terminal  415 , and connector  441 , respectively. Ground connection terminal  316  and cable  361  corresponds to ground connection terminal  416  and cable  461 . As described above, the destination terminal for second communication terminal  4  is first communication terminal  3 . 
       FIG. 8A  is a perspective view of a main part of one example of the installed state of the second communication terminal according to Embodiment 1.  FIG. 8B  is a perspective view of the main part illustrating one example of another installed state of the second communication terminal according to Embodiment 1. In the supply apparatus (charging apparatus  2 ), second conductor  603  electrically connected to first conductor  601  includes core wire  244  (refer to  FIG. 7A ) of internal wire  24  (refer to  FIG. 8A ) that electrically connects between charging plug socket  21  and feeding circuits  23  in the supply apparatus. Therefore, electrode  42  of electrode-attached communication terminal  4  is coupled via electric field to second conductor  603  by being wound around internal wire  24 , as illustrated in  FIG. 8A  and  FIG. 8B . Electrode  42  is wound on sheath  245  around internal wire  24  over sheath  245 . 
     In accordance with the embodiment, electrode  42  surrounds the conductive member in an entire circumference of a circumferential direction of conductive member  60 . That is, in the case that conductive member  60  (second conductor  603 ) includes core wire  244  of internal wire  24 , electrode  42  surrounds conductive member  60  in the entire circumference of the circumferential direction in a cross-section of internal wire  24  perpendicular to extending direction D 24  (lengthwise direction) of internal wire  24 . 
     In accordance with the embodiment, since a wiring between charging apparatus  2  and electric vehicle  1  is single-phase three-wire system 100V wiring, as illustrated in  FIG. 8A , internal wire  24  as conductive member  60  includes neutral line  243  of N phase and a pair of voltage lines  241  and  242  of L1 phase and L2 phase. Neutral line  243  is electrically connected, for example, to a stable potential point, such as the ground. That is, neutral line  243  is grounded. Accordingly, a voltage of neutral line  243  with respect to the ground which is a voltage between neutral line  243  and the stable potential point becomes 0 [V], whereas a voltage of each of voltage lines  241  and  242  with respect to the ground which is a voltage between the stable potential point and each of the pair of voltage lines  241  and  242  becomes 100 [V]. The voltage between one voltage line  241  (L1 phase) and neutral line  243  (N phase) becomes 100 [V]. The voltage between another voltage line  242  (L2 phase) and neutral line  243  (N phase) becomes 100 [V]. The voltage between the pair of voltage lines  241 ,  242  becomes 200 [V]. 
     That is, conductive member  60  includes neutral line  243  and voltage lines  241  and  242 . Electrode  42  is configured to be coupled via electric field only to voltage lines  241  and  242  out of neutral line  243  and voltage lines  241  and  242 . Electrode  42  is not coupled via electric field to neutral line  243  substantially. In the example shown in  FIG. 8A , electrode  42  is wound around two of three internal wires  24  (both voltage lines  241  and  242 ) to bundle the pair of voltage lines  241  and  242  with electrode  42 . On the other hand, in the example shown in  FIG. 8B , electrode  42  is wound only around one voltage line  241  out of the pair of voltage lines  241  and  242 . In the example shown in  FIG. 8B , electrode  42  is wound so as to adhere closely to sheath  245  with almost no gap. 
     Thus, electrode  42  is preferably coupled via electric field only to voltage lines  241  and  242  out of conductive member  60  excluding neutral line  243 . That is, in the electric field communication, since signals are transmitted using the electric field that occurs between conductive member  60  and the reference potential point, neutral line  243  that can be the reference potential point is preferably not included in conductive member  60 . Electrode  42  may be coupled via electric field to both of the pair of voltage lines  241  and  242  as illustrated in  FIG. 8A , and may be coupled via electric field only to one voltage line of the pair of voltage lines  241  and  242 , and may not be coupled via electric field to another voltage line, as illustrated in  FIG. 8B . In comparison of these configurations, the signal reception strength is higher in the configuration shown in  FIG. 8A  (electrode  42  being coupled via electric field to both of the pair of voltage lines  241  and  242 ) than the configuration shown in  FIG. 8B  (electrode  42  being coupled via electric field to only one of the pair of voltage lines  241  and  242 ). 
     However, an aspect of the electric field coupling of electrodes  32  and  42  to conductive member  60  is preferably identical to each other between first communication terminal  3  and second communication terminal  4 . That is, when electrode  32  of first communication terminal  3  is coupled via electric field to both of the pair of voltage lines  151  and  152  (refer to  FIG. 3 ), electrode  42  of second communication terminal  4  is preferably coupled via electric field to both of the pair of voltage lines  241  and  242  (refer to  FIG. 8A ). Meanwhile, when electrode  32  of first communication terminal  3  is coupled via electric field to only one voltage line  151  (refer to  FIG. 4D ), electrode  42  of second communication terminal  4  is preferably coupled via electric field to only one voltage line  241  (refer to  FIG. 8B ). When electrodes  32  and  42  each being coupled via electric field to only one voltage line, the voltage line to which electrode  32  is coupled preferably has the sane phase as the voltage line to which electrode  42  is coupled, but may have different phases (L1 phase and L2 phase) from the voltage line to which electrode  42  is coupled. 
     As a function peculiar to second communication terminal  4  provided in charging apparatus  2  which is the supply apparatus, second communication terminal  4  may have a function to control feeding circuit  23  of charging apparatus  2 . In this case, second communication terminal  4  can switch whether or not to supply electric power from charging apparatus  2  to electric vehicle  1  which is the electric device by, for example, switching turning on and off of switch  231  provided in feeding circuit  23 . In the present exemplary embodiment, second communication terminal  4  has a function to control feeding circuit  23  of charging apparatus  2 . This point will be detailed below. 
     Controller  413  of second communication terminal  4  controls switch  231  to switch turning on and off of switch  231  electrically connected to feeding line  7 . In the case that switch  231  is an electromagnetic relay, controller  413  switches turning on and off of switch  231  by outputting a control signal to an exciting coil of switch  231 . Controller  413  is configured to turn off switch  231  for a communication period for which communication unit  41  communicates with the destination terminal (first communication terminal  3 ). In this case, controller  413  is configured to turn on switch  231  for a period different from the communication period. 
     Controller  413 , similarly to controller  313 , is configured to mainly include an MPU, and to control communication unit  41  (transmitting circuit  411  and receiving circuit  412 ). Controller  413  thus recognizes whether or not communication unit  41  communicates with the destination terminal, that is, whether or not it is in the communication period currently. When determining that communication unit  41  communicates with the destination terminal, that is, it is in the communication period currently, controller  413  turns off switch  231  forcibly in response to the control signal. 
     Switch  231  is connected in feeding line  7  that connects power source  8  to electric vehicle  1 , as described above. Connection and disconnection between power source  8  and electric vehicle  1  are switched along with switching of turning on and off of switch  231 . Communication unit  41  communicates with the destination terminal while charging apparatus  2  is connected to electric vehicle  1  via charging cable  5 . Therefore, for the communication period, while charging apparatus  2  is connected to electric vehicle  1  via charging cable  5 , when controller  413  turns off switch  231 , power source  8  is electrically disconnected from electric vehicle  1 , and electric power supply from power source  8  to electric vehicle  1  is stopped. When controller  413  turns on switch  231 , power source  8  is electrically connected to electric vehicle  1 , and electric power from power source  8  to electric vehicle  1  is supplied. 
     Further, when switch  231  is turned off, while charging apparatus  2  is connected to electric vehicle  1  via charging cable  5 , electric vehicle  1  is electrically disconnected from first line  71  that electrically connects power source  8  to switch  231 . That is, feeding line  7  is divided into first line  71  and second line  72  with switch  231  as a boundary between lines  71  and  72 . First line  71  of feeding line  7  which is on the side of power source  8  from switch  231  is electrically disconnected from second line  72  of feeding line  7  which is on the side of electric vehicle  1  from switch  231  while switch  231  is turned off. Accordingly, for the communication period for which communication unit  41  communicates with the destination terminal, electric vehicle  1  is electrically disconnected from first line  71 . 
     Here, controller  413  continuously turns off switch  231  at least from the beginning the communication period to the end of the communication period. That is, at least for the period for which communication unit  41  communicates with the destination terminal, controller  413  continuously turns off switch  231 . For the period different from the communication period (before the communication period or after the communication period), controller  413  may turn on or off switch  231 . 
       FIG. 9  is a schematic block diagram of the supply apparatus (charging apparatus  2 ) according to Embodiment 1. In accordance with the present embodiment, as illustrated in  FIG. 9 , controller  413  includes input terminal  417  electrically connected to detector  26  that is provided in charging apparatus  2  (supply apparatus) and that detects a state of charging apparatus  2 . Controller  413  is configured to turn off switch  231  depending on a detection result of detector  26  input to input terminal  417  even for the period different from the communication period. In accordance with the present embodiment, detector  26  includes open-close detector  26   a  that detects an opening and closing state of lid  25  of charging apparatus  2 . 
     Open-close detector  26   a  may be implemented by a mechanical switch turned on and off in accordance with opening and closing of lid  25 , and outputs different detection results to input terminal  417  while which lid  25  is closed (hereinafter, referred to as a “closed state”) and while lid  25  is opened (hereinafter, referred to as an “open state”).  FIG. 9  does not illustrate the components of second communication terminal  4  other than communication unit  41 , controller  413 , and input terminal  417 , and does not illustrate the components of charging apparatus  2  other than switch  231  and detector  26 . 
     When the detection result of the detector  26  indicates the open state of lid  25 , controller  413  turns off switch  231  regardless of whether or not it is in the communication period currently. That is, while lid  25  is opened, controller  413  receives a detection result of detector  26  that indicates the opening of lid  25 , and forcibly turns off switch  231 . Accordingly, while lid  25  is opened, power source  8  is electrically disconnected from charging plug socket, and plug  51  is prevented from being plugged or unplugged while energization is performed through charging plug socket  21 . Detector  26  may include not only open-close detector  26   a  but also connection detector  26   b  that detects a connection status of plug  51  of charging cable  5  to charging plug socket  21 , as described above, for example. 
     Timing at which controller  413  turns on switch  231  will be described later (see &lt;Operation of communication system&gt;). 
     That is, communication terminal  40  is provided in the supply apparatus (charging apparatus  2 ) that supplies electric power from power source  8  to the electric device (electric vehicle  1 ) through feeding line  7 , and includes controller  413  and communication unit  41  that communicates with the destination terminal (first communication terminal  3 ) provided in the electric device. Controller  413  controls switch  231  to switch turning on and off of switch  231  electrically connected to feeding line  7 . Feeding line  7  includes first line  71  that electrically connects power source  8  to switch  231 , and second line  72  that electrically connects switch  231  to the electric device. 
     At least one of communication unit  41  and the destination terminal is electrically connected to electrodes  32  and  42 . Electrodes  32  and  42  are located away across a space from conductive member  60  included in feeding line  7  as to be coupled via electric field to conductive member  60 . Communication unit  41  is configured to communicate with the destination terminal by using a transmitted signal via conductive member  60  included in second line  72  of conductive member  60  as a medium. Controller  413  is configured to turn off switch  231  for the communication period for which communication unit  41  communicates with the destination terminal. 
     Electrode-attached communication terminal  4  includes communication terminal  40  to which electrode  42  is added. Electrode  42  is located away via a space from conductive member  60  included in feeding line  7 , so as to be coupled via electric field to conductive member  60 . In electrode-attached communication terminal  4 , communication unit  41  is electrically connected to electrode  42 . 
     &lt;Detail of Electrode-Attached Communication Terminal&gt; 
     The electrode-attached communication terminals will be detailed below. 
     In accordance with the embodiment, the reference potential point of communication unit  41  of second communication terminal  4  is grounded. Specifically, the reference potential point of communication unit  41  which serves as a circuit ground in transmitting circuit  411  and receiving circuit  412  is grounded, for example, by being electrically connected to a body having a stable potential that can be a reference, such as the ground, with an electric conductor. In accordance with the embodiment, similarly to first communication terminal  3 , second communication terminal  4  includes ground terminal  45  functioning as a reference potential point which is to be grounded. Accordingly, communication unit  41  becomes stable because the potential of the reference potential point is identical to the potential of a stable potential point, such as the ground, providing a higher transmission efficiency than the case where the reference potential point is not grounded. In other words, since first communication terminal  3  and second communication terminal  4  transmit the transmission signal, for example, by using the electric field that occurs between conductive member  60  and the ground as described above, the stable reference potential point of communication unit  41  reduces the transmission loss and improves the transmission efficiency. The stable reference potential point of communication unit  41  reduces spurious emission. 
     In the present embodiment, the reference potential point of communication unit  41  is grounded via a frame ground of the supply apparatus. That is, ground terminal  45  which is the reference potential point of communication unit  41  is grounded via the frame ground of charging apparatus  2 . Housing  22  of charging apparatus  2  is made of a conductive metal, and the reference potential point of feeding circuit  23  is electrically connected to housing  22 . Ground terminal  45  which is the reference potential point of communication unit  41  is electrically connected to housing  22  together with the reference potential point of feeding circuit  23 . Furthermore, housing  22  of charging apparatus  2  is grounded by being electrically connected to a body, such as the ground, that has a stable potential with an electric conductor. Accordingly, the reference potential point of communication unit  41  (ground terminal  45 ) is grounded to the body, such as the ground, that has a stable potential via housing  22  which is the frame ground of charging apparatus  2  (see  FIG. 1 ). In charging apparatus  2 , housing  22  may not necessarily have conductivity. When at least a part of housing  22  has conductivity and functions as the frame ground, the reference potential point of communication unit  41  is grounded to the body via housing  22  which is the frame ground of charging apparatus  2 . This configuration allows communication unit  41  to transmit the transmission signal by using the electric field with respect to the frame ground of charging apparatus  2  (potential of housing  22 ). That is, end points of electric force lines that flowing from electrode  42  are converged on the frame ground of charging apparatus  2  (housing  22 ), which provides a stable electric field and reduces the transmission loss, hence improving the transmission efficiency and reducing spurious emission. 
     In accordance with the embodiment, the reference potential point of communication unit  41  is grounded together with neutral line  243 . That is, internal wire  24  as conductive member  60  (second conductor  603 ) of charging apparatus  2  includes neutral line  243  of N phase, as described above. Accordingly, electrode-attached communication terminal  4  has a configuration in which ground electrode  45  is electrically connected to neutral line  243  and is grounded together with neutral line  243 . In the case that neutral line  243  is not grounded, when an electric field (signal) is superimposed on neutral line  243 , interference may occur among a plurality of charging apparatuses  2  via neutral line  243 . The interference is likely to occur when the neutral line of the power source is common to charging apparatuses  2 . When neutral line  243  is grounded as in the embodiment, the potential of neutral line  243  in the charging apparatuses  2  is compulsorily made uniform, and an electric field (signal) component superimposed on the neutral line decreases. Communication unit  41  can transmit the transmission signal by using the electric field that occurs between neutral line  243  and each of voltage lines  241  and  242 , and a distance from a starting point to end point of the electric force line becomes short as compared with the case where the ground is the end point of the electric force line. Therefore, the electric force line becomes less susceptible to an obstacle or the like, which provides stable electric field and reduces the transmission loss, hence improving the transmission efficiency. As a distance from ground electrode  45  to a grounding point of neutral line  243  decreases and a distance from ground electrode  45  to charging apparatus  2  decreases, an effect of stable electric field increases. 
     In the present exemplary embodiment, also in first communication terminal  3  provided in electric vehicle  1 , ground terminal  35  is grounded together with neutral line  153  similarly to second communication terminal  4  described above. That is, internal wire  15  as conductive member  60  in electric vehicle  1  (second conductor  602 ) includes neutral line  153  which is an N phase as described above. Therefore, ground terminal  35  is configured to be electrically connected to neutral line  153  and to be grounded together with neutral line  153 . However, unlike second communication terminal  4 , grounding mentioned here is electrically connected not to the ground or the like, but to conductive part  131 , that is, body ground. This configuration allows communication unit  31  to transmit the transmission signal by using the electric field that occurs between neutral line  153  and each of voltage lines  151  and  152 , stabilizing the electric field and reduce the transmission loss, hence improving the transmission efficiency. 
     Alternatively, in first communication terminal  3  provided in electric vehicle  1 , ground terminal  35  may be electrically insulated from neutral line  153 . This configuration provides electric insulation between neutral line  153  and conductive part  131 , and maintains electric insulation between secondary battery  11  and the battery for electric parts (different from secondary battery  11  for driving). That is, in general, since conductive part  131  is electrically connected to a negative terminal of the battery for electric parts, when neutral line  153  is connected to ground terminal  35 , secondary battery  11  is electrically connected to the battery for electric parts via charging circuit  14 . Meanwhile, the configuration in which ground terminal  35  is electrically insulated from neutral line  153  maintains electric insulation between secondary battery  11  and the battery for electric parts. Also, in electric vehicle  1  in which neutral line  153  is not grounded, the configuration in which ground terminal  35  is electrically insulated from neutral line  153  does not require an operation for grounding neutral line  153 , that is, for electrically connecting neutral line  153  to conductive part  131 , thus improving workability. 
     &lt;Configuration of Communication System&gt; 
     The communication system according to the present embodiment includes first communication terminal  3  and second communication terminal  4  with the above-described configurations. That is, the communication system includes first communication terminal  3  provided in the electric device, and second communication terminal  4  that is provided in the supply apparatus that supplies electric power from power source  8  to the electric device through feeding line  7 , and communicates with first communication terminal  3 . 
     At least one of first communication terminal  3  and second communication terminal  4  includes electrodes  32  and  42 . That is, first communication terminal  3  includes electrode  32  while second communication terminal  4  does not include electrode  32 . Alternatively, first communication terminal  3  does not include electrode  32  while second communication terminal  4  includes electrode  42 . Alternatively, first communication terminal  3  includes electrode  32  while second communication terminal  4  includes  42 . Electrodes  32  and  42  are located away across a space from conductive member  60  included in feeding line  7  as to be coupled via electric field to conductive member  60 . Feeding line  7  includes first line  71  that electrically connects power source  8  to switch  231 , and second line  72  that electrically connects switch  231  to the electric device. Ground terminal  35  is electrically connected to conductive part  131  made of a conductive material in the vehicle. Communication unit  31  is electrically connected to electrode  32  and ground terminal  35 , operates with ground terminal  35  as the reference potential point, and communicates with second communication terminal  4  by using the signal transmitted via conductive member  60  as a medium. 
     Second communication terminal  4  includes communication unit  41  and controller  413 . Communication unit  41  is configured to communicate with first communication terminal  3  by using a signal transmitted via conductive member  60  included in second line  72  of conductive member  60  as a medium. Controller  413  controls switch  231  to switch turning on and off of switch  231 . Controller  413  is configured to turn off switch  231  for a communication period for which communication unit  41  communicates with first communication terminal  3 . 
     In the present embodiment, the electric device is electric vehicle  1  including with secondary battery  11 . The supply apparatus is charging apparatus  2  that supplies electric power to the electric device through the feeding line (charging cable  5 ), and charges secondary battery  11 . 
     &lt;Operation of Communication System&gt; 
     The communication system according to the present exemplary embodiment described above allows charging system  10  to perform the following operations. That is, by mutual communication between first communication terminal  3  provided in electric vehicle  1  (electric device) and second communication terminal  4  provided in charging apparatus  2  (supply apparatus), charging system  10  can exchange signals between electric vehicle  1  and charging apparatus  2 . 
     In charging system  10 , while electric vehicle  1  is electrically connected to charging apparatus  2  via charging cable  5 , electric power is supplied from feeding circuit  23  of charging apparatus  2  to charging circuit  14  of electric vehicle  1 , thereby charging secondary battery  11  of electric vehicle  1 . In charging apparatus  2 , for example, in order to perform billing according to an amount of charging or in order to determine whether electric vehicle  1  is a vehicle that is permitted to receive electric power, performing an authentication process of electric vehicle  1  is considered. Therefore, by using the communication system described above, charging system  10  can exchange signals necessary for the authenticating process of electric vehicle  1  between electric vehicle  1  and charging apparatus  2 . 
     While charging electric vehicle  1 , when electric vehicle  1  is connected via charging cable  5 , charging apparatus  2  first acquires identification information from electric vehicle  1  by communication. The identification information of electric vehicle  1  is information that corresponds uniquely to electric vehicle  1 , and is registered previously in first communication terminal  3  provided in electric vehicle  1 . The identification information is registered, for example, by being set previously at a time of manufacturing of first communication terminal  3 , or by being recorded in a memory of first communication terminal  3  with a dedicated setting device. 
     When electric vehicle  1  is connected to charging apparatus  2  via charging cable  5  and causes first communication terminal  3  to communicate with second communication terminal  4 , first communication terminal  3  starts transmitting the identification information automatically. First communication terminal  3  repetitively transmits the identification information plural times at predetermined time intervals. Second communication terminal  4  acquires the identification information on electric vehicle  1  by receiving at least once the identification information transmitted from first communication terminal  3 . That is, first communication terminal  3  is configured to transmit, to second communication terminal  4 , the identification information unique to the electronic device (electric vehicle  1 ) by the communication with second communication terminal  4 . 
     Upon acquiring the identification information on electric vehicle  1 , second communication terminal  4  verifies the identification information against reference information previously registered. The reference information is identification information formally registered, and is previously registered in second communication terminal  4  provided in charging apparatus  2 . The reference information is registered, for example, by being written in a memory of second communication terminal  4 . Alternatively, in the case that second communication terminal  4  has a communication function with an authentication server, the reference information may be registered previously in the authentication server. In this case, second communication terminal  4  transmits the identification information of electric vehicle  1  to the authentication server, and then, the authentication server authenticates the identification information. 
     Second communication terminal  4  or the authentication server that authenticates the identification information determines that the verification is a success when the registered reference information matches with the acquired identification information. Second communication terminal  4  or the authentication server determines that the verification is a failure when the registered reference information matches with the acquired identification information. When the authentication server authenticates the identification information, the authentication server transmits information on whether the verification of the identification information succeeds or not to second communication terminal  4  as an authentication result of the identification information. Then, when the verification of the identification information succeeds, second communication terminal  4  starts supplying electric power from the supply apparatus (charging apparatus  2 ) to the electronic device (electric vehicle  1 ). On the other hand, second communication terminal  4  is configured not to cause electric power to be supplied from the supply apparatus (charging apparatus  2 ) to the electronic device (electric vehicle  1 ) when the verification of the identification information does not succeed. That is, depending on the authentication result of the identification information, second communication terminal  4  controls feeding circuit  23  of charging apparatus  2  and switches whether or not to supply electric power from charging apparatus  2  to electric vehicle  1 . 
     Specifically, in second communication terminal  4 , controller  413  controls switch  231  to switch whether or not to supply electric power from charging apparatus  2  to electric vehicle  1 . When the verification of the identification information succeeds, controller  413  turns on switch  231  to cause charging apparatus  2  to supply electric power to electric vehicle  1 . When controller  413  turns on switch  231 , power source  8  is electrically connected to electric vehicle  1 , and electric power is supplied from power source  8  to electric vehicle  1  through charging apparatus  2 . 
     However, in the present embodiment, controller  413  is configured to turn off switch  231  for the communication period as described above. Further, controller  413  turns off switch  231  when the detection result of detector  26  indicates the open state of lid  25  even for the period different from the communication period. In this case, controller  413  turns off switch  231  when the detection result of detector  26  indicates the open state of lid  25 , regardless of whether or not it is in the communication period currently. Controller  413  turns off switch  231  for the communication period regardless of the detection result of detector  26 . Accordingly, at the timing when the verification of the identification information succeeds, controller  413  confirms whether or not it is in the communication period currently and further confirms the detection result of detector  26 , and controls switch  231 . That is, controller  413  turns on switch  231  when the verification of the identification information succeeds for a period different from a communication period and further lid  25  is in the closed state. 
     &lt;An Operation of Communication System&gt; 
       FIG. 10  is a block diagram of the communication system according to Embodiment 1 for illustrating an operation of the communication system. The communication system according to the present embodiment includes plural charging apparatuses  2  which are plural supply apparatuses. In the example illustrated in  FIG. 10 , n number of electric vehicles  101 ,  102 , . . .  10   n  are parked in a parking lot in which n number of charging apparatuses  201 ,  202 , . . .  20   n  are installed side by side. The n number of charging apparatuses  201 ,  202 , . . .  20   n  have the same configurations, and each of the apparatuses is provided with second communication terminal  4  that can be a destination terminal of first communication terminal  3 . Hereinafter, to distinguish second communication terminal  4  provided in charging apparatus  201  from second communication terminal  4  provided in charging apparatus  202 , second communication terminal  4  of charging apparatus  201  is referred to as “second communication terminal  401 ”, and second communication terminal  4  of charging apparatus  202  is referred to as “second communication terminal  402 ”. Second communication terminal  4  provided in charging apparatus  20   n  is referred to as “second communication terminal  40   n”.  Similarly, first communication terminal  3  of electric vehicle  101  is referred to as “first communication terminal  301 ”, first communication terminal  3  of electric vehicle  102  is referred to as “first communication terminal  302 ”, and first communication terminal  3  of electric vehicle  10   n  is referred to as “first communication terminal  30   n”.    
     Here, each of the n number of electric vehicles  101 ,  102 , . . .  10   n  is connected to respective one of the n number of charging apparatuses  201 ,  202 , . . .  20   n  in a one-to-one correspondence via second line  72  (including charging cable  5 ). This configuration allows each electric vehicle  1  to receive electric power supplied from corresponding charging apparatus  2 . Here, each of the n number of charging apparatuses  201 ,  202 , . . .  20   n  is connected to one power source  8  via respective one of first lines  71  of charging apparatuses  201 ,  202 , . . .  20   n.  Accordingly, as illustrated in  FIG. 10 , plural (n number of) charging apparatuses  201 ,  202 , . . .  20   n  are electrically connected to each other via first lines  71  of charging apparatuses  201 ,  202 , . . .  20   n.    
     Accordingly, while first line  71  is electrically connected to second line  72  in each of the n number of charging apparatuses  201 ,  202 , . . .  20   n,  second lines  72  of the n number of charging apparatuses  201 ,  202 , . . .  20   n  are electrically connected to each other through first lines  71  of charging apparatuses  201 ,  202 , . . .  20   n.  Here, first communication terminal  3  and second communication terminal  4  communicate with each other by using a transmission signal transmitted via conductive member  60  included in second line  72  of conductive member  60  as a medium. Accordingly, while second lines  72  are electrically connected to each other among the n number of charging apparatuses  201 ,  202 , . . .  20   n,  the transmission signal may leak among the n number of charging apparatuses  201 ,  202 , . . .  20   n.  For example, the transmission signal transmitted by first communication terminal  301  of electric vehicle  101  to second communication terminal  401  of charging apparatus  201  may leak to second communication terminal  402  of charging apparatus  202  through first line  71 . Further, in this case, when second communication terminal  402  of charging apparatus  202  communicates with first communication terminal  302  of electric vehicle  102 , interference may occur between charging apparatus  201  and charging apparatus  202 . 
     The interference mentioned here means a phenomenon in which signals (transmission signals) from plural electric vehicles  1  (first communication terminals  3 ) mix, and plural charging apparatuses  2  (second communication terminals  4 ) cannot receive the signals normally. For example, in the above example, charging apparatus  202  may receive the signal from electric vehicle  102  and the signal that leaks from electric vehicle  101  through first line  71  simultaneously. In this case, charging apparatus  202  may not determine which signal is from corresponding electric vehicle  102 , that is, the signal from electric vehicle  102  connected to second line  72 . That is, the interference occurs. When such interference occurs, for example, when attempting to acquire the identification information by communication from electric vehicle  1 , charging apparatus  202  acquires the identification information of two electric vehicles  101  and  102  simultaneously. 
     In the communication system according to the present embodiment, as described above, controller  413  turns off switch  231  for the communication period, thereby preventing such leakage of the transmission signal and occurrence of interference. That is, when switch  231  is turned off, first line  71  on the side of power source  8  from switch  231  is electrically disconnected from second line  72  on the side of electric vehicle  1  from switch  231  while switch  231  is turned off. Controller  413  turns off switch  231  to disconnect first line  71  from second line  72  for the communication period for which first communication terminal  3  and second communication terminal  4  communicate with each other. For example, during communication between first communication terminal  301  and second communication terminal  401 , controller  413  of second communication terminal  401  turns off switch  231  of charging apparatus  201 , thereby disconnecting second line  72  between charging apparatus  201  and electric vehicle  101  from first line  71 . Therefore, the transmission signal transmitted by first communication terminal  301  to second communication terminal  401  is prevented from leaking to second communication terminal  402  through first line  71 , thereby and occurrence of interference between charging apparatus  201  and charging apparatus  202  is inhibited. For the period different from the communication period, communication terminal  40   n  may turn on switch  231 , whereby first line  71  and second line  72  are connected to each other and electric power is supplied to electric vehicle  10   n.    
     &lt;Advantageous Effects&gt; 
     In the configuration using wireless communications as described in PTL 2, when plural devices that can be communication partners exist near one device, it is difficult to perform one-to-one communication. For example, when two electric vehicles approach one charging apparatus, both of the two electric vehicles can communicate with the charging apparatus, and thus, it is difficult for the charging apparatus to identify which of the two electric vehicles is to be charged. 
     Electrode-attached communication terminal  3   a,  communication terminal  30 , and the communication system according to the present exemplary embodiment described above can perform electric field communication with the destination terminal by using conductive member  60  as a medium with the destination terminal and exchanging signals. Since the electric field communication mentioned here mainly uses the electric field that attenuates in proportion to the third power of a distance when propagating through space, communication can be established between terminals connected via a particular communication path instead of an unspecified path in space, although non-contact. That is, in the electric field communication, since the signal that propagates through space immediately attenuates and the signal propagates mainly through conductive member  60  with little attenuation, communication between terminals connected via the particular communication path is established. Therefore, conductive member  60  as the communication path allows electrode-attached communication terminal  3  to establish communication with the destination terminal only after the electronic device is connected to the supply apparatus via feeding line  7  (second line  72 ). This results in an advantage that one-to-one communication can be performed even when the supply apparatus and the electric device exist within a short distance with a one-to-many or plural-to-one relationship. 
     Moreover, since electrode  32  is coupled via electric field to conductive member  60 , for example, electrode  32  can positively superimpose the electric field component of the transmission signal applied by transmitting circuit  311  on second conductor  602  or first conductor  601 . Since electrode  32  is coupled via electric field to conductive member  60  by being wound on the sheath around internal wire  15  or charging cable  5 , electrode-attached communication terminal  3   a  can be easily installed in the electronic device by post-installation. That is, since electrode  32  is coupled via electric field to the medium (conductive member  60 ), electrode-attached communication terminal  3   a  can communicate even if electrode  32  is not directly connected to the medium, and can be easily installed by post-installation. Since it is unnecessary to process internal wire  15  or charging cable  5  for installing electrode  32 , electrode-attached communication terminal  3   a  once installed can be moved. Alternatively, even when electrode-attached communication terminal  3   a  is installed to the electronic device from the beginning (at the time of manufacturing of the electronic device), electrode-attached communication terminal  3   a  which requires neither soldering nor special connectors reduces installation costs or time and effort. 
     Effects as described above can be produced not only in electrode-attached communication terminal  3  and communication terminal  30 , but also in electrode-attached communication terminal  4  and communication terminal  40  having the identical basic configuration. 
     In the present embodiment, as a function peculiar to second communication terminal  4  provided in charging apparatus  2  which is the supply apparatus, second communication terminal  4  has a function to control feeding circuit  23  of charging apparatus  2 . That is, controller  413  of second communication terminal  4  controls switch  231  to switch turning on and off of switch  231  electrically connected to feeding line  7 . Controller  413  is configured to turn off switch  231  for the communication period for which communication unit  41  communicates with the destination terminal (first communication terminal  3 ). In this configuration, for the communication period for which first communication terminal  3  and second communication terminal  4  communicate with each other, controller  413  turns off switch  231 , thereby first line  71  is electrically disconnected from second line  72 . In other words, while first line  71  is electrically connected to second line  72 , first communication terminal  3  and second communication terminal  4  do not communicate with each other. 
     Therefore, although first communication terminal  3  and second communication terminal  4  communicate with each other by using a transmission signal transmitted via conductive member  60  included in second line  72  of conductive member  60  as a medium, switch  231  prevents leakage of the transmission signal to first line  71 . As a result, for example, even when plural charging apparatuses  2  are electrically connected to each other via first line  71  as in the operation example described above, plural charging apparatuses  2  are electrically disconnected from each other, substantially, by turning off switch  231 . This configuration prevents interference among plural charging apparatuses  2 . 
     The interference mentioned here, as described above, means a phenomenon in which signals (transmission signals) from plural electric vehicles  1  (first communication terminals  3 ) mix, and plural charging apparatuses  2  (second communication terminals  4 ) cannot receive the signals normally. That is, in the configuration of the present embodiment, plural charging apparatuses  2  are electrically disconnected from each other, substantially, by turning off switch  231 , and the communication paths for the electric field communication between plural charging apparatuses  2  are disconnected. Accordingly, when there are plural pairs of charging apparatus  2  and electric vehicle  1  connected to each other via second line  72 , each pair is electrically independent, and occurrence of interference among plural charging apparatuses  2  is inhibited. Since the interference is likely to be problematic as a number of charging apparatuses  2  connected to one power source system (first line  71 ) increases, the effect of the present exemplary embodiment increases in which occurrence of interference can be inhibited as the number of charging apparatuses  2  connected to one power source increases. 
     Switch  231  is not limited to the electromagnetic relay, and may be implemented by a semiconductor switching device, such as a P-intrinsic-N (PIN) diode or a field effect transistor (FET) using gallium arsenide (GaAs). However, switch  231  is preferably implemented by a mechanical switch, such as the electromagnetic relay, in which contacts are mechanically opened and closed to be turned on and off. That is, unlike general wired communication, since the electric field communication mainly uses the electric field, isolation performance of switch  231  to the signal when switch  231  is turned off is higher in the mechanical switch than in the semiconductor switching device. Accordingly, in the case that switch  231  is implemented by the mechanical switch, the signal disconnection effect between the plural charging apparatuses  2  increases more than a semiconductor switching device. 
     In the electric field communication, a signal component that propagates through space attenuates in proportion to the third power of the distance. Accordingly, even when leakage of the signal occurs by propagation through space, influence on the interference of the leakage signal is very small, and the effect of inhibiting the interference by turning off switch  231  is sufficient. In fact, the signal leaked by propagating through space between plural charging apparatuses  2  attenuates at more than about 20 [dB], that is, about 1/100 with respect to signal electric power. 
     In the configuration of the present embodiment, noise that flows from first line  71  into second communication terminal  4  is reduced. That is, when switch  231  is turned off to electrically disconnect first line  71  from second line  72 , the noise that flows from first line  71  to second communication terminal  4  is reduced. For example, in the operation example described above, while charging apparatus  201  charges electric vehicle  101 , an AC-DC converter in charging circuit  14  of electric vehicle  101  generates noise, and the noise may be transmitted to first line  71  via charging apparatus  201 . In this case, switch  231  of charging apparatus  202  connected to the same first line  71  as charging apparatus  201  is turned off to prevent the noise on first line  71  from flowing into second communication terminal  402  of charging apparatus  202 . Further, when first line  71  is electrically connected to various devices via a switchboard or the like, switch  231  of charging apparatus  2  is turned off to prevent the noise generated in these various devices from flowing into second communication terminal  4  of charging apparatus  2  via first line  71 . The noise that flows from first line  71  into second communication terminal  4  is reduced in this way, thereby reducing influence of the noise on communication between first communication terminal  3  and second communication terminal  4 . 
     Furthermore, switch  231  of charging apparatus  2  is turned off to prevent first communication terminal  3  or second communication terminal  4  itself from becoming a noise source. That is, since first communication terminal  3  and second communication terminal  4  each output predetermined electric power during communication, the electric power may become noise. Switch  231  of charging apparatus  2  is turned off to prevent the noise from flowing into first line  71 , and reduces influence of the noise on various devices and other charging apparatus  2  (second communication terminal  4 ) connected to first line  71 . The influence of the noise mentioned here, unlike the interference described above, includes a case where electric field communication itself is prevented between other charging apparatus  2  (second communication terminal  4 ) and electric vehicle  1  (first communication terminal  3 ). 
     Furthermore, ground terminal  35  which is the reference potential point of communication unit  31  is electrically connected (grounded) to conductive part  131  of electric vehicle  1 . In other words, ground terminal  35  connected to conductive part  131  allows communication unit  31  to be grounded to the body. This configuration reduces impedance of the reference potential point of communication unit  31  as compared with a case where ground terminal  35  is not electrically connected to conductive part  131  (electrically isolated), thus stabilizing potential of the reference potential point. This provides stable electric field near electrode  32  and reduces the transmission loss, thus improving the transmission efficiency. In the communication between first communication terminal  3  and second communication terminal  4 , electric field communication that mainly uses the electric field becomes more dominant. This configuration reduces electromagnetic waves that do not propagate through second conductor  602  or first conductor  601  and are emitted to space, hence reducing spurious emission. This results in an advantage of stable electric field used for the electric field communication, improving the transmission efficiency of the transmission signal and reducing spurious emission. 
     That is, while electrode-attached communication terminal  3  communicates with the destination terminal, when communication unit  31  applies a signal to electrode  32 , for example, an electric field occurs between conductive member  60  and the ground, as described above. At this moment, if ground terminal  35  is not connected to conductive part  131 , any of conductive part  131  that exists near electrode  32 , neutral line  153 , and the ground can be the end points of the electric force lines that start from electrode  32 , which may lead to unstable electric field. Meanwhile, when ground terminal  35  which is the reference potential point of communication unit  31  is connected to conductive part  131 , the end points of the electric force lines that start from electrode  32  is converged on conductive part  131 . This configuration stabilizes electric field used for the electric field communication and improves the signal transmission efficiency. Also, as a surface area of conductive part  131  increases, the effect produced by connecting ground terminal  35  to conductive part  131  increases. This is caused by inhibiting a ground bounce generated from an electric field coupling portion. 
     The following will describe a result of confirmation about to what extent the transmission efficiency is improved during transmission of the transmission signal from first communication terminal  3  to second communication terminal  4 , by electrically connecting ground terminal  35  which is the reference potential point of communication unit  31  to conductive part  131  actually. Ground terminal  35  connected to conductive part  131  significantly reduces the transmission loss and improves the transmission efficiency, as compared with a case where ground terminal  35  is not connected to conductive part  131 . In a certain vehicle model, while the transmission loss in a case where ground terminal  35  is not connected to conductive part  131  is 50 [dB] while the transmission loss in a case where ground terminal  35  is connected to conductive part  131  is 20 [dB]. In other vehicle models, ground terminal  35  connected to conductive part  131  improves the transmission loss, for example, from 55 [dB] to 40 [dB], or improves the transmission loss from 50 [dB] to 35 [dB]. 
     In the present embodiment, ground terminals  35  and  45  are not essential for electrode-attached communication terminals  3  and  4 , and ground terminals  35  and  45  may be omitted if appropriate. When ground terminals  35  and  45  are omitted in communication terminals  30  and  40 , ground connection terminals  316  and  416  may be omitted. 
     In the communication system according to the present exemplary embodiment, the electric device is electric vehicle  1  equipped with secondary battery  11 , and the supply apparatus is charging apparatus  2 . Charging apparatus  2  supplies electric power to the electric device through the feeding line (charging cable  5 ), and charges secondary battery  11 . This configuration allows the communication system to perform the communication between electric vehicle  1  and charging apparatus  2  in charging system  10 . Therefore, in charging system  10 , for example, in order to perform billing according to an amount of charging, or in order to determine whether or not electric vehicle  1  is a vehicle to which charging is permitted, the authentication process of electric vehicle  1  can be performed. 
     Moreover, since communication with the destination terminal is established only after the electric device and the supply apparatus are connected to each other via the feeding line (charging cable  5 ), even when plural charging apparatuses  2  are installed side by side, electrode-attached communication terminal  3  can perform one-to-one communication between electric vehicle  1  and charging apparatus  2 . Even when plural electric vehicles  1  are positioned near one charging apparatus  2 , one-to-one communication between electric vehicle  1  and charging apparatus  2  can be performed. As a result, this communication system can perform one-to-one communication even when plural devices that can be communication partners exist near the one device. 
     Here, as in the present embodiment, first communication terminal  3  is preferably configured to transmit, to second communication terminal  4 , the identification information unique to the electric device (electric vehicle  1 ) by communication with second communication terminal  4 . Accordingly, for example, in order to perform billing according to the amount of charging, or in order to determine whether or not electric vehicle  1  is a vehicle to which charging is permitted, the authentication process of electric vehicle  1  can be performed by using the identification information transmitted from first communication terminal  3  to second communication terminal  4 . 
     Second communication terminal  4  is configured not to cause the supply apparatus (charging apparatus  2 ) to supply electric power to the electric device (electric vehicle  1 ) when the verification of the identification information does not succeed. Therefore, when the verification of the identification information does not succeed due to a device other than authorized electric vehicle  1  connected or other reasons, charging apparatus  2  does not supply electric power, preventing useless electric power supply to an unauthorized device. 
     Electric vehicle  1  is used as the electric device in the communication system, and includes first communication terminal  3 . Therefore, even when plural devices (charging apparatuses  2 ) that can be communication partners exist near one electric vehicle  1 , electric vehicle  1  can perform one-to-one communication with charging apparatus  2  actually connected via charging cable  5 . 
     Charging apparatus  2  is used as the supply apparatus in the communication system, and includes second communication terminal  4 . Therefore, even when plural devices (electric vehicles  1 ) that can be communication partners exist near one charging apparatus  2 , charging apparatus  2  can perform one-to-one communication with electric vehicle  1  actually connected via charging cable  5 . 
     The electric device is not limited to electric vehicle  1 , and the supply apparatus is not limited to charging apparatus  2 . That is, the electric device may have a configuration that receives electric power supplied from the supply apparatus through a feeding line, and the electric device may be a device, such as a smart phone, a tablet terminal, or a digital camera, including a secondary battery. 
     Exemplary Embodiment 2 
       FIG. 11  is a perspective view of a main part of a first communication terminal according to Embodiment 2 for illustrating one example of an installation state thereof. An electrode-attached communication terminal according to the embodiment is different from the electrode-attached communication terminal according to Embodiment 1 in a coupling state of electrode  32  to conductive member  60 . Hereinafter, components identical to those of Embodiment 1 are denoted by the same reference numerals, and their description will be omitted. 
     In accordance with the embodiment, electrode  32  of electrode-attached communication terminal  3  (a first communication terminal) provided in electric vehicle  1  (a vehicle) is configured to be coupled via electric field to all of neutral line  153  and voltage lines  151  and  152 , as illustrated in  FIG. 11 . That is, according to the embodiment, similarly to Embodiment 1, conductive member  60  includes neutral line  153  and voltage lines  151  and  152 . While electrode  32  is coupled via electric field only to voltage lines  151  and  152  out of neutral line  153  and voltage lines  151  and  152  in accordance with Embodiment 1, electrode  32  is coupled via electric field to all of neutral line  153  and voltage lines  151  and  152  in accordance with the present embodiment. 
     In accordance with the present embodiment, in detail, as internal wire  15  of electric vehicle  1 , one pair of voltage lines  151  and  152  which are an L1 phase and an L2 phase, and neutral line  153  which is an N phase constitute one internal cable  150 . That is, internal cable  150  includes three internal wires  15  in total including the pair of voltage lines  151  and  152  and neutral line  153  which are covered with an insulating sheath (an outer covering) and bundled into one cable. Accordingly, in the vehicle (electric vehicle  1 ), one internal cable  150  electrically connects charging inlet  12  to charging circuit  14 . As illustrated in  FIG. 11 , electrode  32  performs electric field coupling to conductive member  60  (second conductor  602 ) by being wound on the sheath around internal cable  150  without processing internal cable  150 . 
     The configuration of the present exemplary embodiment described above allows electrode  32  to be installed over the outer covering (sheath) of internal cable  150  even when plural internal wires  15  are bundled and constitute the cable (internal cable  150 ) inside the vehicle (electric vehicle  1 ). Therefore, an operator who installs electrode-attached communication terminal  3  allows electrode  32  to be coupled via electric field to core wire  154  of internal wire  15  as second conductor  602  without processing internal cable  150 , and post-installation in electric vehicle  1  is easy. 
     In the configuration of the present embodiment, an effect is especially increased produced by ground terminal  35  of first communication terminal  3  provided in electric vehicle  1  being grounded together with neutral line  153 . That is, as in the present exemplary embodiment, in the configuration in which electrode  32  of first communication terminal  3  provided in electric vehicle  1  is coupled via electric field to neutral line  153 , an electric field occurs between neutral line  153  and the ground. In charging apparatus  2  provided with second communication terminal  4 , neutral line  243  is grounded. Accordingly, a region with an unstable electric field may exist in a communication path between first communication terminal  3  and second communication terminal  4 . In this configuration, ground terminal  35  grounded (body ground) together with neutral line  153  decreases impedance of a reference potential point of communication unit  31  and provides stable electric field, thus significantly improving transmission efficiency. 
     In the configuration of the present exemplary embodiment, as described in the first exemplary embodiment, an effect provided by a reference potential point of communication unit  41  being grounded together with neutral line  243  increases. This is because interference among plural charging apparatuses  2  described above occurs conspicuously in a portion of conductive member  60  that is coupled via electric field to electrode  42  due to an electric field (signal) more positively superimposed on neutral line  243 . That is, in the configuration of the present exemplary embodiment, the reference potential point of communication unit  41  is grounded together with neutral line  243  to reduce an electric field (signal) component superimposed on neutral line  243  and significantly prevent interference among plural charging apparatuses  2 . 
     Other configurations and functions are similar to configurations and functions of the first exemplary embodiment. 
     Exemplary Embodiment 3 
       FIG. 12  is a perspective view of a main part of a first communication terminal according to Exemplary Embodiment 3 for illustrating an example of an installation state thereof. An electrode-attached communication terminal according to the present embodiment is different from the electrode-attached communication terminal according to Embodiment 1 in a coupling state of electrode  32  to conductive member  60 . Hereinafter, components identical to those of the terminal according to Embodiment 1 are denoted by the same reference numerals, and their description will be omitted. 
     In the present exemplary embodiment, as illustrated in  FIG. 12 , electrode  32  of electrode-attached communication terminal  3  (a first communication terminal) provided in electric vehicle  1  (an electronic device) is coupled via electric field to core wire  534  of electric wire  53  included in charging cable  5 , first conductor  601 . In the present exemplary embodiment, similarly to Embodiment 1, conductive member  60  includes neutral line  533  and voltage lines  531  and  532 . In the present exemplary embodiment, electrode  32  is coupled via electric field to all of neutral line  533  and voltage lines  531  and  532  similarly to Embodiment 2. 
     In detail, charging cable  5  includes neutral line  533  which is an N phase and one pair of voltage lines  531  and  532  which are an L1 phase and an L2 phase which are bundled into one cable with an insulating sheath (outer covering) thereon. Accordingly, one charging cable  5  electrically connects the electronic device (electric vehicle  1 ) to the supply apparatus (charging apparatus  2 ). As illustrated in  FIG. 12 , electrode  32  performs electric field coupling to conductive member  60  (first conductor  601 ) by being wound on the sheath around charging cable  5  without processing charging cable  5 . 
     The configuration of the present exemplary embodiment described above allows electrode  32  to be installed to charging cable  5 , which is the feeding line, over the outer covering (sheath). Therefore, an operator who installs electrode-attached communication terminal  3  can cause electrode  32  to be coupled via electric field to core wire  534  of electric wire  53  as first conductor  601  without processing charging cable  5 . 
     The configuration in which electrode  32  is installed to charging cable  5  as described in the present exemplary embodiment is particularly useful in electric vehicle  1  with the configuration in which charging cable  5  is not detachable. That is, electric vehicle  1  may lack charging inlet  12  to which connector  52  of charging cable  5  is detachably connected and employ the configuration in which charging cable  5  is electrically connected to charging circuit  14  directly. In electric vehicle  1  with such a configuration, charging cable  5  is accommodated inside car body  13  except when secondary battery  11  is charged, and when secondary battery  11  is charged, charging cable  5  is pulled out of car body  13  and is connected to charging apparatus  2 . In electric vehicle  1  with such a configuration, charging cable  5  is typically provided at a position where a user of electric vehicle  1  can touch, hence simplifying an operation of installing electrode  32  to charging cable  5 . 
     The configuration of the present exemplary embodiment is applicable not only to first communication terminal  3  but also to second communication terminal  4 . That is, electrode  42  of electrode-attached communication terminal  4  (a second communication terminal) provided in charging apparatus  2  (the supply apparatus) may be coupled via electric field to core wire  534  of electric wire  53  included in charging cable  5 , which is first conductor  601 . This configuration is particularly useful in charging apparatus  2  with the configuration in which charging cable  5  is not detachable. That is, charging apparatus  2  may lack charging plug socket  21  to which plug  51  of charging cable  5  is detachably connected and employ the configuration in which charging cable  5  is electrically connected to feeding circuit  23  directly. In this kind of charging apparatus  2 , charging cable  5  is typically provided at a position where a user of charging apparatus  2  can touch, hence particularly simplifying an operation of installing electrode  42  in charging cable  5 . 
     Other configurations and functions are similar to configurations and functions of Embodiment 1. 
     Exemplary Embodiment 4 
     A communication system according to Exemplary Embodiment 4 is different from the communication system according to Embodiment 1 in that only one of first communication terminal  3  and second communication terminal  4  includes electrode  32  (or  42 ) coupled via electric field to conductive member  60 . Components identical to those of the terminal according to Embodiment 1 are denoted by the same reference numerals, and their description will be omitted. 
     The present exemplary embodiment describes an example in which, only first communication terminal  3  provided in electric vehicle  1  (an electric device) out of first communication terminal  3  and second communication terminal  4  includes electrode  32 . In the present embodiment, in second communication terminal  4  provided in charging apparatus  2  (a supply apparatus), communication unit  41  is electrically connected directly to conductive member  60  (at least one of first conductor  601  and second conductor  603 ). 
     In this configuration, between first communication terminal  3  and second communication terminal  4 , only electrode  32  of first communication terminal  3  and conductive member  60  are coupled to each other while not contacting each other, and except for this coupling, a communication path is configured to be directly connected via conductive member  60 . This results in a smaller transmission loss between first communication terminal  3  and second communication terminal  4  than a case where both electrode  32  of first communication terminal  3  and electrode  42  of second communication terminal  4  are coupled to conductive member  60  while not contacting each other. That is, for example, in the case that charging apparatus  2  includes second communication terminal  4  from the beginning (at a time of manufacturing of the device), post-installation of second communication terminal  4  in the device (charging apparatus  2 ) is not needed. The configuration of the present exemplary embodiment reduces the transmission loss. 
     In this configuration, since electrode  32  of first communication terminal  3  provided in electric vehicle  1  is coupled to conductive member  60  while not contacting, electric vehicle  1  does not necessarily include first communication terminal  3  from the beginning (at the time of manufacturing of the electric vehicle). Also, processing for installing electrode  32  around a feeding line through which a large electric current flows in electric vehicle  1  is not necessary, hence simplifying an operation for installation of first communication terminal  3  and reducing a cost of electric vehicle  1 . In particular, for a two-wheel vehicle or the like which is relatively inexpensive among electric vehicles  1 , the effect of cost reduction of electric vehicle  1  is large. Also, first communication terminal  3  can be easily installed in vehicles that have already appeared on the market by post-installation, and is applicable to a lot of vehicle models without involving system changes. 
     The configuration of the present exemplary embodiment is not limited to the above-described example. Only second communication terminal  4  out of first communication terminal  3  and second communication terminal  4  which is provided in charging apparatus  2  (a supply apparatus) may include electrode  42 . In this case, in first communication terminal  3  provided in electric vehicle  1  (an electric device), communication unit  31  is electrically connected directly to conductive member  60  (at least one of first conductor  601  and second conductor  602 ). 
     In this configuration, between first communication terminal  3  and second communication terminal  4 , only electrode  42  of second communication terminal  4  is coupled to conductive member  60  while not contacting conductive member  60 , and except for this coupling, a communication path is to be formed that is directly connected via conductive member  60 . This results in a smaller transmission loss between first communication terminal  3  and second communication terminal  4  than a case where both electrode  32  of first communication terminal  3  and electrode  42  of second communication terminal  4  are coupled to conductive member  60  while not contacting. That is, for example, in the case that electric vehicle  1  includes first communication terminal  3  from the beginning (at a time of manufacturing of the device), post-installation of first communication terminal  3  in the device (electric vehicle  1 ) is not needed, and thus employment of the configuration of the present exemplary embodiment reduces the transmission loss. 
     Other configurations and functions are similar to configurations and functions of Embodiment 1. Also, the configuration of the present exemplary embodiment is applicable in combination with the configuration of each of Embodiments 2 and 3, in addition to the configuration of Embodiment 1. 
     Exemplary Embodiment 5 
       FIG. 13  is a plan view illustrating an electric vehicle and charging apparatus that use a communication system according to Exemplary Embodiment 5. The communication system according to the present exemplary embodiment is different from the communication system according to Embodiment 1 in that communication unit  31  has a function to adjust transmission strength of a signal (transmission signal) so as to prevent interference among plural charging apparatuses  2 . Hereinafter, components identical to those of the terminal according to Embodiment 1 are denoted by the same reference numerals, and their description will be omitted. 
     In the present exemplary embodiment, as illustrated in  FIG. 13 , plural charging apparatuses  2  which are supply apparatuses are installed side by side. In the example illustrated in  FIG. 13 , as the plural supply apparatuses, two charging apparatuses  2 , which are charging apparatus  201  ( 2 ) as a first supply apparatus and charging apparatus  202  ( 2 ) as a second supply apparatus, are installed side by side. Electric vehicle  1  which is an electric device is configured to receive electric power supplied from the first supply apparatus (charging apparatus  201 ) of the plural supply apparatuses (charging apparatuses  201  and  202 ). 
     That is, the present exemplary embodiment assumes a situation in which electric vehicle  1  is parked in a parking lot in which plural charging apparatuses  201  and  202  are installed side by side. In this situation, electric vehicle  1  is connected via charging cable  5  to charging apparatus  201  (first supply apparatus) which is one of plural charging apparatuses  201 ,  202 . This configuration allows electric vehicle  1  to receive electric power supplied from charging apparatus  201  (first supply apparatus) connected via charging cable  5 . Charging apparatus  201  which is the first supply apparatus and charging apparatus  202  which is the second supply apparatus are, for example, installed adjacent to each other, and have the same configuration as each other. Each of the apparatuses is provided with second communication terminal  4  that can be a destination terminal of first communication terminal  3 . Hereinafter, to distinguish second communication terminal  4  provided in charging apparatus  201  from second communication terminal  4  provided in charging apparatus  202 , second communication terminal  4  of charging apparatus  201  is referred to as “second communication terminal  401 ”, and second communication terminal  4  of charging apparatus  202  is referred to as “second communication terminal  402 ”. 
     Here, communication unit  31  of first communication terminal  3  provided in electric vehicle  1  adjusts the transmission strength of the transmission signal to cause radiated electromagnetic field strength to be equal to or less than a predetermined value in second supply apparatus (charging apparatus  202 ) different from first supply apparatus (charging apparatus  201 ) of the plural supply apparatuses. The following details a reason therefor. 
     Ground terminal  35  which is a reference potential point of communication unit  31  electrically connected to conductive part  131  improves transmission efficiency via electric field communication using conductive member  60  as a medium; however, this may simultaneously increase a radiated electromagnetic field that is output from communication unit  31  and propagates through space. This radiated electromagnetic field may also reach charging apparatus  202  to which electric vehicle  1  is not connected (second supply apparatus). When second communication terminal  402  provided in charging apparatus  202  receives this radiated electromagnetic field, interference occurs between charging apparatus  201  and charging apparatus  202 . Therefore, in the present exemplary embodiment, communication unit  31  is configured to prevent interference by adjusting the transmission strength of the transmission signal as to cause the radiated electromagnetic field strength in charging apparatus  202  to be equal to or less than the predetermined value. 
     In more detail, communication unit  31  adjusts the transmission strength (transmission power) of the transmission signal in transmitting circuit  311  as to cause the radiated electromagnetic field strength near electrode  42  of second communication terminal  402  in charging apparatus  202 , which is a second supply apparatus, to be equal to or less than the predetermined value. This configuration allows charging apparatuses  201  and  202  to isolate the transmission signal from electric vehicle  1  connected via charging cable  5  (hereinafter referred to as “desired signal”) from a transmission signal from electric vehicle  1  that is not connected (hereinafter referred to as “leakage signal”). This prevents interference between plural charging apparatuses  2 . 
     Here, the predetermined value that is an upper limit of the radiated electromagnetic field strength in second communication terminal  402  may be previously determined and stored in a memory of second communication terminal  402 , and may be a value that changes in response to an operation of a variable resistor or the like. The predetermined value may be 10 [dBμV/m]. Example 1 and Example 2 of the predetermined value of the present exemplary embodiment will be described below. 
     EXAMPLE 1 
     In Example 1, the predetermined value is determined as to cause reception strength of the transmission signal (reception power) in second communication terminal  402  provided in charging apparatus  202  (second supply apparatus) to be smaller than reception strength in second communication terminal  401  provided in charging apparatus  202  (first supply apparatus). This configuration produces a difference in the reception strength of the transmission signal transmitted from first communication terminal  3  between charging apparatus  201  and charging apparatus  202 . In other words, a value obtained by converting the radiated electromagnetic field strength near second communication terminal  402  of charging apparatus  202  into the reception strength of the transmission signal in second communication terminal  402  becomes lower than the reception strength of the transmission signal in second communication terminal  401 . An antenna gain of electrode  42  may be reflected on the converted value. 
     In this case, second communication terminal  4  can distinguish the desired signal from the leakage signal, for example, by comparing the reception strength of the transmission signal with a predetermined threshold. That is, by determining that the transmission signal is the desired signal when the reception strength of the transmission signal is equal to or higher than the threshold, and by determining that the transmission signal is the leakage signal when the reception strength is lower than the threshold, second communication terminal  4  can extract only the desired signal, thereby suppressing interference. 
     Also, comparing the transmission signal received by second communication terminal  401  with the transmission signal received by second communication terminal  402  also allows the desired signal to be distinguished from the leakage signal. In this case, for example, a higher level apparatus capable of communicating with both second communication terminals  401  and  402  compares the reception strength of the transmission signal between both second communication terminals  401  and  402 . That is, when second communication terminal  401  and second communication terminal  402  receive the signal transmitted from one electric vehicle  1  simultaneously, the higher level apparatus compares the reception strength of the transmission signal in second communication terminal  401  with the reception strength of the transmission signal in second communication terminal  402 . Then, the higher level apparatus determines that second communication terminal  4  with the higher reception strength receives the desired signal, and that second communication terminal  4  with the lower reception strength receives the leakage signal, thereby suppressing interference. 
     In this configuration, since a difference only needs to arise in the reception strength of the transmission signal between charging apparatus  201  and charging apparatus  202 , communication unit  31  of first communication terminal  3  can set relatively high transmission strength of the transmission signal. Therefore, Example 1 provides relatively high reception strength of the transmission signal (desired signal) in second communication terminal  401  and high transmission efficiency between electric vehicle  1  and charging apparatus  201  which are connected via charging cable  5 . 
     EXAMPLE 2 
     In Example 2, the predetermined value is set to cause the reception strength of the transmission signal in second communication terminal  402  provided in charging apparatus  202  (second supply apparatus) to be lower than reception sensitivity of second communication terminal  402 . The reception sensitivity mentioned here is the minimum reception strength that allows second communication terminal  402  to secure reception quality required for communication. That is, second communication terminal  402  does not primarily receive the transmission signal whose reception strength is lower than the reception sensitivity as a signal. Here, the reception sensitivity is equal between second communication terminal  401  and second communication terminal  402 . In other words, the value obtained by converting the radiated electromagnetic field strength near second communication terminal  402  of charging apparatus  202  into the reception strength of the transmission signal in second communication terminal  402  becomes lower than the reception intensity of second communication terminal  4 . An antenna gain of electrode  42  may be reflected on the converted value. 
     In this case, since second communication terminal  4  does not receive the leakage signal as a signal, second communication terminal  4  can receive only the desired signal. That is, unlike Example 1, Example 2 allows second communication terminal  4  to extract only the desired signal without distinguishing the desired signal from the leakage signal by comparison of the reception strength of the transmission signal, thereby suppressing interference. Therefore, Example  2  simplifies processes after receipt of the transmission signal. 
     In the present exemplary embodiment, plural charging apparatuses  2 , which are plural supply apparatuses, only need to be installed side by side, and the number of charging apparatuses  2  is not limited to two but may be three or more. For example, when six charging apparatuses  2  are installed side by side, one electric vehicle  1  is connected to one charging apparatus  2  out of these six charging apparatuses  2  via charging cable  5 , and receives electric power supplied from one connected charging apparatus  2 . Therefore, one charging apparatus  2  out of these six charging apparatuses  2  which is connected to electric vehicle  1  via charging cable  5  is a first supply apparatus. In this case, other supply apparatuses are other charging apparatuses  2  different from the first supply apparatus described above, and are not required to be adjacent to charging apparatus  2  as the one supply apparatus. 
     Other configurations and functions are similar to configurations and functions of Embodiment 1. The configuration of the present exemplary embodiment is applicable in combination with the configuration of each of Embodiments 2, 3, and 4, in addition to the configuration of Embodiment 1. 
     Exemplary Embodiment 6 
       FIG. 14  is a block diagram of a communication system according to Exemplary Embodiment 6. In  FIG. 14 , components identical to those of the system according to Embodiment 1 illustrated in  FIG. 1  are denoted by the same reference numerals. The communication system illustrated in  FIG. 14  includes communication terminals  3   b  and  4   b  instead of communication terminals  3  and  4  of the communication system according to Embodiment 1 illustrated in  FIG. 1 . 
     Communication terminal  3   b  further includes grounding capacitor  35   c  connected in series between ground connection terminal  3116  of communication unit  31  and ground terminal  35  of communication terminal  3  illustrated in  FIG. 1 . In other words, ground terminal  35  connected to conductive part  131  allows communication unit  31  to be grounded to the body via grounding capacitor  35   c  in high-frequencies although communication unit  31  is not grounded to the body in a direct-current frequency. This configuration reduces impedance of a reference potential point of communication unit  31  compared with a case where ground terminal  35  of communication unit  31  is not electrically connected to conductive part  131  (electrically isolated), hence providing a stable potential of the reference potential point of communication unit  31 . 
     Communication terminal  4   b  further includes grounding capacitor  45   c  connected in series between ground connection terminal  416  of communication unit  41  and ground terminal  45  of communication terminal  4  illustrated in  FIG. 1 . In other words, ground terminal  45  connected to housing  22  allows communication unit  41  to be grounded to the body via grounding capacitor  45   c  in high frequencies although communication unit  41  is not grounded to the body in a direct-current frequency. This configuration reduces impedance of the reference potential point of communication unit  41  compared with a case where ground terminal  45  of communication unit  41  is not electrically connected to housing  22  (electrically isolated), thus providing a stable potential of the reference potential point of communication unit  41 . 
     In the communication system illustrated in  FIG. 14 , both communication terminals  3  and  4  of the communication system according to Embodiment 1 illustrated in  FIG. 1  are replaced by communication terminals  3   b  and  4   b.  In the communication system according to Embodiment 6, communication terminal  3  out of communication terminals  3  and  4  of the communication system according to Embodiment 1 illustrated in  FIG. 1  may be replaced by communication terminal  3   b  and may constitute the communication system together with communication terminal  4 . Also, communication terminal  4  out of communication terminals  3  and  4  of the communication system according to Embodiment 1 illustrated in  FIG. 1  may be replaced by communication terminal  4   b  and may constitute the communication system together with communication terminal  3 . 
     Grounding capacitor  35   c  produces a similar effect by being connected in series between the reference potential point of communication unit  31  and ground terminal  35 , instead of between ground connection terminal  316  of communication unit  31  and ground terminal  35 . For example, grounding capacitor  35   c  may be connected in series between connection terminal  316  and each of reference potential point  311   a  of transmitting circuit  311 , reference potential point  312   a  of receiving circuit  312 , reference potential point  313   a  of controller  313 , and reference potential point  314   a  of power supply circuit  314 . Grounding capacitor  45   c  produces a similar effect by being connected in series between the reference potential point of communication unit  41  and ground terminal  45 , instead of between ground connection terminal  416  of communication unit  41  and ground terminal  45 . For example, grounding capacitor  45   c  may be connected in series between ground connection terminal  416  and each of reference potential point  411   a  of transmitting circuit  411 , reference potential point  412   a  of receiving circuit  412 , reference potential point  413   a  of controller  413 , and reference potential point  414   a  of power supply circuit  414 . 
     Other configurations and functions are similar to configurations and functions of Embodiment 1. The configuration of the present exemplary embodiment is applicable in combination with the configuration of each of Embodiments 2, 3, 4, and 5, in addition to the configuration of Embodiment 1.