A power supply device according to the invention includes: a power switch; a rectification diode generating an output current by rectifying a current supplied according to a switching operation of the power switch; and a switch control circuit generating an output current estimation voltage corresponding to the output current using a detection sense voltage corresponding to a sense voltage that depends on a switch current flowing to the power switch and a compensated discharge period. The compensated discharge period is a period from the peak of a discharge current flowing to the rectification diode to an instant at which the discharge current becomes zero current.