A current resonance type switching power circuit includes a rectifying circuit for rectifying commercial power, a smoothing circuit having a choke coil and a smoothing capacitor for smoothing the output of the rectifying circuit, a switching circuit unit for rendering intermittent the voltage output from the smoothing circuit, and a resonance circuit which includes a primary winding of an insulation transformer and a resonance capacitor and is supplied with a switching output of the switching circuit unit, wherein the resonance circuit is connected to a line between the rectifying circuit and the smoothing circuit so that the resonance output thereof is superposed on the choke coil.