When a valve lift signal is received from a control unit (10), two of the coils (18a-18d) in a stepping motor (18) are energized to regulate the opening of the valve (14). A predetermined time after the completion of the opening regulation of the valve (14), the energization method for the stepping motor (18) is switched from a two-phase energization to a single-phase energization. This suppresses the generation of heat in the coil and the current consumption while the rotation is stopped.
