A switching power supply device includes: a rectifier circuit to which an AC input voltage is input; an input smoothing circuit smoothing a DC input voltage output from the rectifier circuit; a power converter circuit converting the DC input voltage and outputs an output voltage; an overvoltage detection circuit generating an input overvoltage detection signal which is activated when the DC input voltage is higher than a first reference voltage level; and a discharge circuit discharging stored charge stored in the input smoothing circuit. The power converter circuit includes a switching element. Switching of the switching element is stopped and discharging of the stored charge is started, with activation of the input overvoltage detection signal serving as a trigger, and when the input overvoltage detection signal is subsequently inactivated, the discharging is stopped and the switching of the switching element is resumed.