In the present invention, switching circuits connected in middle points of power supply lines of a three-phase alternating-current power supply are switched to cause currents to intermittently flow on primary windings of a transformer, a voltage generated on a secondary winding is rectified and smoothed, and then is outputted to a load. The switching circuits each include: a series circuit including a first primary winding, a bidirectional switch and a second primary winding, which are connected in series in this order; a drive circuit power supply generating circuit generating a direct-current positive voltage and a direct-current negative voltage by use of an alternating-current power supply voltage applied between two ends of the series circuit; and a drive circuit performing on-off drive of the bidirectional switch. A reference potential point of the bidirectional switch is connected to a reference potential point of the drive circuit power supply generating circuit.