PURPOSE: To generate a precision stabilizing power source, also to great current, by rectifying and smoothing pulse generated by switching DC voltage with an active element, and by arranging two sets of circuits generating DC, in parallel with each other to combine output.

CONSTITUTION: A commercial power source 1 is rectified 2a, and smoothed 2b, and DC voltage Ein for output is generated. Pulse generated by switching the output Ein with the first pulse generation circuit 3aA is rectification- smoothed 3bA via the first insulating transformer 3gA, and DC voltage Eout1 for output is generated. The output Ein is processed in the second system as in the first system, and DC output Eout2 is obtained. Output Eout obtained by arranging the DC output Eout1 and Eout2 in series is fed to a load 4. The output voltage Eut is detected 3c, and is compared with the reference voltage of a reference voltage generation circuit 3e, and control signal for output is generated from a control circuit 3d, and the pulse generation circuits 3aA, 3aB are controlled. As a result, the power transistor of a large capacity is used, and the stable DC power source of high precision is easily obtained.