To provide a power circuit capable of attaining highly stable output DC voltage even if an AC voltage range is wide in obtaining DC output of low voltage by rectifying AC power voltage.

This power circuit comprises a power supply transformer of which the primary winding is connected with a commercial AC power supply and which generates AC voltage stepped down to a secondary winding, a bridge rectifying circuit of which the input terminal is connected to between one end and the other of the secondary winding, a first and a second capacitors connected in series to between one end and the other of the output terminal of the rectifying circuit, a switch connected to between a junction of the first and the second capacitors and the other end of the transformer, and a control circuit which turns off the switch when an inputted AC voltage level is within a prescribed voltage range and turns on the switch when the AC voltage is out of the prescribed voltage range. Bridge rectification or voltage doubler rectification is activated by turning on/of the switch.