To prevent the lowering of torque and the number of revolution even when the number of turns of a coil is increased and a current is reduced, by variably controlling the frequency of the commutation or interruption of an applied output independently without using the rotational-position information of the shaft of a motor.

A rotary switch 4 is formed in a shape that nine rings in total are fixed to a shaft 41, a pulley 42 is installed to the shaft 41 and a belt is stretched between the pulley 42 and a pulley 22 mounted on the shaft 21 of an auxiliary motor 2, and the shaft 41 of the rotary switch 41 can be rotated by turning the auxiliary motor 2. The DC output of a battery 3 is commutated by revolving the rotary switch 4 by the auxiliary motor 2 and the coils of each phase of a motor 1 are supplied with the commutated DC output and the coils are rotated, but the frequency of the commutation of a current fed to the coils of each phase can be controlled by adjusting the number of revolution of the auxiliary motor 2 at an arbitrary value. Accordingly, the number of turns of the motor is increased, and the current is reduced while the lowering of the number of revolution and torque can be prevented.