PURPOSE: To control output voltage at high precision with little consumption power till light-weight loading, by controlling frequency interrupting the input voltage of a switching power circuit, according to the condition of a detected load.

CONSTITUTION: The voltage of a load current detection resistance 8 is divided with resistances 18, 19, and the input to the + terminal of a comparation 15 is provided. The input of grand voltage for reference voltage to - terminal is provided via a resistance 20. By comparing the degree of the voltage of the + terminal with the degree of hysteresis voltage determined by the output voltage of resistances 19, 21 and an auxiliary power source 22, the output of low degree or high degree is generated from a comparator 15, and a transistor TR14 is turned OFF or ON. A relay 13 is made or broken, and a resistance 12 and a resistance 11 are connected in series or short-circuited, and the switching frequency of a control circuit 9 is heightened or lowered. As a result, when a load is lowered, then it is switched with high frequency, and the output voltage of high precision is generated, and consumption power is reduced.