A conversion control part controls a converted DC voltage of a voltage converting part. The converted DC voltage is supplied to first and second amplifying parts each including a FET power transistor. At least one of first power transistors of first power amplifying parts and at least one of second power transistors of second power amplifying parts perform a full ON operation, thereby analoguely altering a current path from the converted DC voltage of the voltage converting part to plural-phase windings. This configuration reduces powerless and vibration of a motor.