A power-receiving device includes: a power-receiving circuit; a cylindrically shaped first member; a power-receiving coil connected via wire to the power-receiving circuit, and provided on the cylinder side-surface of the first member; and a resonance coil provided so as to be capable of moving freely along the cylinder side-surface in the direction of rotation around the cylinder-center axis of the first member. Therein, the power-receiving coil and the resonance coil are joined by electromagnetic induction.
