To secure a mounting space and reduce cost to achieve a regenerative operation and a power operation that do not affect the operation of a motor.

In regenerative operation, a regenerative power accumulating/discharging unit 50 controls a transistor drive circuit 70 to change a regenerative power charging transistor 52 restricted on current supply by first and second transistor current limiting circuits 54 and 60, from an active region to a saturated region to cause the regenerative power charging transistor 52 to charge a regenerative power accumulating capacitor 51. In power operation, the regenerative power accumulating/discharging unit 50 controls the regenerative power accumulating capacitor 51 to discharge its accumulated charges to an inverter 30 via a regenerative power discharging diode 53.