To improve an input power factor and eliminate a waveform distortion by achieving an unneeded amount of resistance for an element without adding a complex additional circuit and another switching element in a power supply device with a switching means for adjusting power to be fed to a load.

An AC power supply PS is rectified by a rectification circuit Rec1, a DC power supply obtained by smoothing with a smoothing capacity C0 is switched by a switching element S1, an energy is accumulated in an inductor Ls, and the energy of the inductor Ls is discharged to a smoothing capacitor C0 via a diode D1 and at the same time is transferred to a load and a capacitor C1 via a current-limiting element Z1 and a rectification element Rec2. In this case, a capacitor Cs and a diode D0 are added and a period where current flows from the AC power supply PS is increased, thus improving an input power factor and eliminating a waveform distortion.