A switching regulator which does not require a capacitor having large time constant as a soft start circuit, reduces variation of the soft start time and the time until a start of a power source voltage stabilizing controlThe output voltage signal of the soft start circuit is set to a step voltage signal which increases or decreases stepwise at a predetermined rate. A changing period of the step voltage signal is set to a predetermined period after a power source is turned ON. The changing period of the step voltage of the output signal of the soft start circuit is made larger than the predetermined period according to a timing of changing of the PWM pulse output from “H” to “L” or “L” to “H” after an initial period, and after the power source is turned ON by monitoring the PWM pulse output by a detection circuit.