A clutch mechanism moving together with an actuator allows coupling or decoupling an inner rotor to or from a power shaft, thereby controlling a rotation angle. This structure allows a polarity of a magnetic pole of the inner rotor to be the same as that of an opposing magnetic pole of an outer rotor when the motor is driven at a low rpm, so that magnetic fluxes inter-linking with windings can be increased, which results in greater torque. When the motor is driven at a high rpm, the structure allows the polarity of the magnetic pole of the inner rotor to be different from that of the opposing magnetic pole of the outer rotor, so that an amount of leakage flux is increased, and the magnetic fluxes inter-linking with the winding are decreased. As a result, an induction voltage is lowered and a high rpm range is widened.