PURPOSE: To simplify constitution of a voltage stabilizing circuit, by a method wherein terminal impedance of a second output transformer is controlled corresponding to detected output impedance.

CONSTITUTION: The output from a DC power source 2 is supplied through a switching element 11, a step-up and step-down transformer 13 and a rectifier 14 to a first load 3. A control circuit 12 controls the switching element 11 to hold the output voltage constant. Power to a second load 4 of small capacity is supplied from the transformer 13 through a transformer 15 and peak rectifier 6. A terminal impedance control circuit 7 operates to adjust terminal impedance 5 of the transformer 15 so that the output voltage becomes a specified value.