An active electrode and a passive electrode are electrically field-coupled with an active electrode and a passive electrode provided in a power transmission device, respectively. Power in a high frequency voltage excited on the active electrode and the passive electrode is supplied to a mobile unit via a step-down transformer, a rectification smoothing circuit, and a DC-DC converter. A CPU turns off switches when wireless communication is carried out. The passive electrode functions as a booster antenna that is magnetically field-coupled with an antenna coil. A high frequency signal outputted from an RF circuit is transmitted via the antenna coil and the passive electrode, and a high frequency signal transmitted from the power transmission circuit is inputted, via the passive electrode and the antenna coil, to the RF circuit.