To attain a power supply which rises quickly and produced at a lower price, and is capable of stopping the output of a partial power supply circuit.

A control circuit 7 of a voltage drop chopper circuit 5 as the power supply circuit compares a threshold value which is preset through voltage dividing, by the resistor R5 and resistor R6 with a triangular wave formed in the control circuit 7 by closing the switch SW1. When a triangular wave exceeds a threshold value a pulse is output to supply a current to the base of a transistor Q2 of the voltage drop chopper circuit 5. A voltage is dropped through turning on/off of the transistor Q2, is then smoothed by a capacitor C4, and is then output from output terminals 6, 6. When it is desired to stop the output of the voltage drop chopper circuit 5, a switch SW1 is opened to compare the high threshold with the triangular wave formed in the control circuit 7. Since the triangular wave does not exceed the threshold value, a current is not supplied to the base of transistor Q2 of the voltage drop chopper circuit 5, and thus no output is produced from the output terminals 6, 6.