PURPOSE: To detect a period of time during which an overcurrent limitation works, by using a D-type FF receiving outputs of SRFF and PWM comparator, and a transistor which is turned ON and OFF by the output of the D-type FF.

CONSTITUTION: When an output signal D of SRFF 4 is on a low level at the time of falling of an output signal E of a PWM comparator 7, an output signal G of a D-type FF 22 also is on a low level and causes the charging of a monitoring time setting capacitor 28 with a constant current from a constant current power source 24 through a transistor 25. After the charging is conducted for a certain period of time and the voltage of a terminal 27 reaches a reference voltage 29, an output signal I from a comparator 30 is transferred to a high level so that a latching circuit 31 operates and its output becomes a signal J. After that, when the overcurrent state is over, the signal G shifts to a high level to return to the initial state. In this manner, it is possible to decrease the numbers of external parts and the terminals of a switching regulator controlling IC.