Switching power supply device

A main control circuit includes a PWM comparator that compares a contrast voltage generated according to a feedback voltage with a ramp voltage having a periodically varying voltage value, and causes an output stage circuit to perform a switching action based on a result of the comparison in the PWM control. A feedback path switch is inserted in a feedback path for propagating a signal according to the feedback voltage to the PWM comparator. The main control circuit controls, upon switching from sleep control that stops the switching action to the PWM control, within a specific period equal to one or more periods of the PWM control, the feedback path switch off and sets a voltage within a variation range of the ramp voltage as an initial voltage for the contrast voltage to thereby start a switching action and controlling the feedback path switch on after the specific period.