A power supply device disclosed in the present specification has an output portion which generates an output voltage from an input voltage by means of on-off control of an output transistor and feeds the output voltage to a load, an output feedback controller which drives the output portion by performing output feedback control, and a detector which detects, by means of an electromagnetic induction method, a ripple component in a monitoring target current resulting from the on-off control of the output transistor. The output feedback controller performs the output feedback control based on the result of detection by the detector.