PURPOSE: To compensate the voltage drop by a cable without providing a remote sensing line by getting the voltage drop by a cable from the difference of output DC voltage between an auxiliary DC converter and a DC converter and adding it to reference voltage and making its result reference voltage.

CONSTITUTION: Since a current scarcely flows to the auxiliary smoothing circuit 5 of an auxiliary rectifying circuit 4, there is no voltage drop by resistance. Therefore, if one takes the difference between the DC voltage Vb of the auxiliary smoothing circuit 5 and the output voltage Va and amplifies it, the voltage proportionate to the output current can be gotten at the output of the amplifying circuit 6, and if one adds this voltage to reference voltage with the addition circuit 32 of a voltage stabilizing control circuit 3 and takes the difference with the output voltage Va with a differential amplifier 30 and controls a PWM driving circuit 31, the output voltage Va increases in proportion to the output current. Accordingly, if one sets this amplification factor A1, according to the change of the output current and the change of the voltage drop of a cable, the load current can be controlled to be constant regardless of the change of the output current.