To provide a power circuit which can maintain its efficiency irrespective of the hour rate of "a light load state" or "an overcurrent stop state", related to a power circuit.

A power circuit, which has a switching means that is driven by both or either of inputted first DC power and second DC power generated by to the AC power induced in the auxiliary winding of a transformer and supplies the primary winding of the transformer with this DC power intermittently and supplies power to the outside via the secondary winding of the transformer, is equipped with a rectifying means which rectifies the AC power induced in the auxiliary winding and generates third DC power and a power replenishing means which supplies a power conversion control means with third DC power in a period when the DC power supplied for the drive of the switching means surpasses the predetermined threshold out of the first DC power.