Each DC/DC converter includes a transformer, first and second switching circuits each formed of a plurality of legs having a plurality of semiconductor switching elements, capacitors, a discharge circuit connected in parallel to the secondary side capacitor, and a bypass switch for bypassing the capacitor. When detecting a malfunction in semiconductor switching elements, a control circuit turns OFF all of the semiconductor switching elements, and controls the bypass switch after discharge of the capacitor through the discharge circuit, so that the capacitor is bypassed.