PURPOSE: To get a DC-DC.CONV, which can supply enough high gate voltage and does not cause distortion, by equipping it with a rectifying means, which rectifies the voltage of the drain of a MOS-FET, and a rectifying means for rectified output, and putting the output to the power source voltage of a driving circuit.

CONSTITUTION: The drain voltages VD1 and VD2, which are taken out of the respective drains Ds of MOS-FET Q1 and Q2, are rectified with a rectifying circuit (7) comprised of diodes CD5 and CD6 so as to get Voltage VC1, and this is rectified further with a rectifying circuit (8) comprised of capacitors C6 and C7 and a resistor R3, and this is supplied as the B power of a driving circuit (2). Therefore, chattering ingredients (11a) and (11b), which occur with the inductance ingredients, etc., of a transformer T1 during switching, phase distorted waveform ingredients (12), which occur at the zero cross position when composing switching waveform, and others are removed completely by the rectifying circuits (7) and (8).