A power factor correction circuit includes; a series circuit connected to a positive-electrode output terminal P1 and negative-electrode output terminal P2 of a full-wave rectifying circuit B1, which rectifies an having current power-supply voltage of an alternating current power-supply Vac1, and including a booster winding 5a and a wind-up winding 5b wound on a booster reactor L1, a diode D1 and a smoothing capacitor C1; a series circuit, connected between the positive-electrode output terminal P1 and the negative-electrode output terminal P2 and having the booster winding 5a, a ZCS reactor L2 and a switch Q1; a diode D2 connected between a junction, between the switch Q1 and the ZCS reactor L2, and the smoothing capacitor C1; and a control circuit 10 that controllably turns the switch Q1 on and off for controlling an output voltage of the smoothing capacitor C1 to a given voltage.