PURPOSE: To prevent an output voltage from being changed even in the transition period of a changeover in a power-supply circuit which comprises a plurality of load voltage outputs and in which any one desired output voltage is controlled to be constant by changing over objects to be controlled.

CONSTITUTION: A power-supply circuit is provided with a changeover device 35 which selects any one desired output voltage out of output voltages of a plurality of load output terminals 5, 6 so as to be input to an output-voltage detection circuit 25. In the changeover device 35, Zener diodes and capacitors are connected in parallel across a plurality of input ends (A, B) and an output end (C), an output voltage from a desired load output terminal is selected by a changeover signal to be input by a changeover-signal input end 15 from the outside, and the output voltage is input to the output-voltage detection circuit 25. Then, a control circuit 4 controls the on-off operation of a switching element 3 in such a way that the output voltage becomes constant on the basis of the output signal of the output-voltage detection circuit 25.