PURPOSE: To provide a multi-output switching power unit which can prevent the sharp drop of the output voltage of an auxiliary-output power source circuit when a load becomes lighter and, at the same time, can suppress the occurrence of losses on the outputting route.

CONSTITUTION: An auxiliary-output power source circuit 9 is provided with a choke rectifier circuit 4, capacitor rectifier circuit 19, switching circuit 20, etc., and is constituted in such a way that, when the output voltage V2 of the circuit 9 becomes higher than a set reference voltage, the switching circuit 20 is turned off and the output of its output-side auxiliary coil 15 is supplied to a load (b) through the rectifier circuit 4. When a load (a) becomes lighter and the turned-on period of a switch element 6 becomes shorter, and then, the output voltage V2 becomes lower than the reference voltage, the switching circuit 20 is turned on and the output from the intermediate tap of the coil 15 is stably supplied to the load (b) under a voltage which is nearly equal to the reference voltage through the rectifier circuit 4 irrespective of the turned-on period of the switch element 6. Thus the sharp drop of the voltage V2 is avoided when the load (b) becomes lighter.