Electric motor with multiple rotors in a concentrically circular arrangement around a rotation axis of the electric motor

An electric motor comprising an inner periphery side rotor provided with inner peripheral permanent magnets with unlike poles, which are disposed alternately along a circumferential direction of the inner periphery side rotor, an outer periphery side rotor provided with outer peripheral permanent magnets with unlike poles, which are disposed alternately along a circumferential direction of the outer periphery side rotor, and a rotating device that varies a relative phase between the inner periphery side rotor and the outer periphery side rotor by rotating at least the inner periphery side rotor or the outer periphery side rotor around the rotational axis. The outer peripheral side rotor is arranged such that a rotational axis thereof is coaxial with a rotational axis of the inner periphery side rotor. The rotating device sets a variable width of the relative phase between the inner periphery side rotor and the outer periphery side rotor within a range of an electrical angle of below 180°.