PURPOSE: To decrease the number of solid-state relays, by providing a solid-state relay section between output terminals of a full wave rectifying circuit and a smoothing capacitor.

CONSTITUTION: A full wave rectifying circuit 35 is connected to input terminals 31, 32 where a commercial AC power supply is applied, via main switches 33, 34 interlocked with each other. The 1st output terminal b1 of this rectifying circuit 35 is connected to a signal input terminal c1 of a solid-state relay section 36. The 2nd output terminal b2 of the rectifying circuit 35 is connected to a power output terminal 38 via a smoothing capacitor 37. A signal output terminal c2 of the section 36 is connected to this power supply output terminal 38. A control output of a switch controlling section 39 is applied to control terminals c3, c4 of the section 36.