The peak current flowing to the switching device drops in a no-load state with PWM control, but because the number of switching operations is constant regardless of the load, further reducing power consumption is difficult. The switching power supply device has a PWM signal generator for generating a PWM signal, a switching device Q1 for switching the first supply voltage VIN based on the PWM signal, converters for outputting the difference between a second supply voltage and a reference voltage as a difference signal, and an intermittent oscillation control circuit for stopping the switching operation of the first switching device when the difference signal is less than a predetermined first threshold value (Vp1). The PWM signal generator changes the pulse width based on the difference signal to generate the PWM signal.