An object of the present invention is to suppress deterioration in detection accuracy during power feeding in the detection of the metallic foreign object using the antenna coil. A metallic foreign object detector includes: an antenna coil; a capacitor that constitutes a resonance circuit RC together with the antenna coil; a power supply that applies voltage to the resonance circuit to generate a vibration signal in the resonance circuit; a determination circuit that determines the presence/absence of a metallic foreign object based on the waveform of the vibration signal; a resonance capacitor switch inserted into the resonance circuit; and a control circuit that controls the open/close state of the resonance capacitor switch. The control circuit brings the resonance capacitor switch into a closed state responding to the power supply starting application of voltage to the resonance circuit.