Electric-field-coupled wireless electric power transmission system and power receiving device using same

A power receiving device (200) of an electric power transmission system is provided with an overvoltage suppression means (70) connected in parallel to a resonance circuit (50). The overvoltage suppression means (70) is configured from an impedance element. The impedance of the impedance element is set to a value so as to suppress an increase in voltage between at least a pair of power receiving electrodes (41, 42) relative to a case in which the impedance element is not connected, in the process whereby the coupling capacitance (Cm) between power transmission electrodes (31, 32) and the power receiving electrodes (41, 42) changes to substantially zero from the value thereof when the power transmission electrodes (31, 32) and the power receiving electrodes (41, 42) are in a predetermined positional relationship that occurs during normal power transmission.