To stably supply input power voltage to a ramp driver.

This circuit includes insulation converter transformers T1, T2 as an insulation converter transformer in which the switching output of a primary side switching converter is supplied to its primary side. The insulation converter transformer T1 is for supplying a secondary side DC output voltage to a load. The insulation converter transformer T2 transfers the switching output of the primary side switching converter supplied to a resonance circuit comprising a primary winding N11 and a resonance capacitor C2 to the secondary side as a resonance output. An input voltage of the ramp driver 3 is supplied by using the resonance output transferred to the secondary side. Thus, the input voltage of a level which sufficiently satisfies rated input voltage can be supplied to the ramp driver, independent of a level of rectified and smoothed voltage gained by rectifying and smoothing a commercial AC power.