A switching power supply circuit comprises a switching element for controlling the on/off state of an input power supply according to a drive pulse generated on the basis of a clock pulse having a prescribed period. Breakdown of circuit elements due to current superposition is effectively prevented by detecting current flowing through the switching element and flywheel current, and comparing these detected results with a first and second reference value, respectively. An overcurrent detection circuit detects that the current flowing through a transistor for controlling the on/off state of the input power source has reached a first reference value, a flywheel current detection circuit detects flywheel current, an overcurrent protection operation is performed for turning off the transistor based on the detected output of the overcurrent detection circuit, and the transistor is turned on during the overcurrent protection operation at the timing of the clock pulse after the flywheel current detected by the flywheel current detection circuit has reached the second reference value.