When an abnormality is detected by an abnormality detection unit, a first switching stop device turns OFF all of switching elements connected to one arm of either an upper arm or a lower arm of a power converter, and turns ON all of the switching elements connected to the arm, which are not turned OFF; when the abnormality is continuously detected even after operating the first switching stop device, a second switching stop device turns ON or turns OFF the switching elements connected to the upper arm and the lower arm so that the turn-ON and the turn-OFF are reversed to the operation by the first switching stop device; and when the abnormality is continuously detected even after operating the second switching stop device, a third switching stop device turns OFF all of the switching elements in the upper arm and the lower arm.