METALLIC FOREIGN OBJECT DETECTOR, WIRELESS POWER TRANSMITTING DEVICE, WIRELESS POWER RECEIVING DEVICE, AND WIRELESS POWER TRANSMISSION SYSTEM

An object of the present invention is to reduce the possibility of failure in the detection of metallic foreign object. A metallic foreign object detector includes a sensor part having at least one antenna coil that receives a magnetic field or current to generate a vibration signal a vibration time length measurement circuit that measures a vibration time length indicating the length of time required for the vibration of the vibration signal output from the sensor part corresponding to a predetermined wavenumber larger than 1, and a determination circuit that determines the presence/absence of a metallic foreign object approaching the antenna coil based on the vibration time length and a criterion vibration time length which is the vibration time length obtained in the absence of the approaching metallic foreign object.