PURPOSE: To protect a switching power source circuit and load circuit by stopping the operation of the switching power source circuit when the value of a current signal continuously exceeds a prescribed reference voltage by at least two times.
CONSTITUTION: The inverted output signal FFQ of a flip flop circuit 19 opens or closes a switch 34 and connects a constant-current source 35 with an external capacitor 37 and external resistor 38. The capacitor 37 is set so that it can exceed the reference voltage VL of a comparator 36 when a comparator 20 is continuously inverted five times. When the value of the voltage signal V 1 S of a transistor 25 exceeds a reference voltage VS the output signal FFQ of the flip flop circuit 19 becomes a high level through the comparator 20 and a charging current is supplied to the external capacitor 37. When the charging is continuously made to the capacitor 37 more than five times, a switching power source circuit stops its operation and the transistor 25 is turned off.