A metallic foreign object detector, used in a wireless power transmission system that transmits power using an alternating magnetic field, includes antenna coils that generate a vibration signal by receiving a magnetic field or current, one or more capacitors that constitute a resonance circuit together with each of the antenna coils, and a detection part that detects a metallic foreign object by sequentially using the antenna coils. The detection part has detection modes that detect the presence/absence of the metallic foreign object based on changes in mutually different characteristics of the resonance circuit. The detection part selects one mode from the detection modes in accordance with at least one of the power feeding state of the wireless power transmission system and the position of each of the plurality of antenna coils and performs the detection of the metallic foreign object in the selected detection mode.