When a control circuit (6) detects an overcurrent, the control circuit (6) conducts ON-OFF control of a switching element that is switchable in the forward/reverse directions such that, when the control circuit (6) is in a mode wherein the current flowing until then is reduced, and a mode wherein current is made to flow through either one of the diodes, a switching element that is connected in parallel to the current-flowing diode is turned ON. Specifically, a switching element (4a) of the upper arm of a phase wherein current flows out from a series connection point between the upper and lower arms thereof to a motor (2) is turned OFF, a switching element (4d) of the lower arm of the phase is turned ON, switching elements (4e, 4f) of the lower arms of phases wherein currents flow in from the motor (2) through the series connection points thereof are turned OFF, and switching elements (4b, 4c) of the upper arms of those phases are turned ON. In such a way, current flowing through a diode connected in parallel to a switching element is limited even when an overcurrent is generated, to protect the diode from deterioration or damages due to the overcurrent.