A contactless power feeding device that supplies electric power to a power receiving device without contact includes: a power transmitting circuit that transmits alternating-current power; and a power transmitting resonator including a power transmitting coil. The input impedance of the power transmitting resonator is set low in a facing state in which a power receiving coil included in the power receiving device faces the power transmitting coil, and the input impedance of the power transmitting resonator is set high in a non-facing state in which the power receiving coil does not face the power transmitting coil.