To perform inexpensive power factor improvement control of an input power source, when AC power is rectified and DC power is supplied.

A converter is provided with a reference apparatus 12 which outputs an output voltage reference signal, a proportional/integrator 13 which proportions/integrates the deviation between the output signal of the reference apparatus 12 and an output voltage signal, and a current following-up circuit 9 which receives as an input of an output current reference signal an added signal of the output signal of the proportional/integrator to a signal obtained by multiplying the output signal of a rectifier 2 by a coefficient set beforehand, and controls the switching of a switching device 5 so as to follow up an output current reference signal, receiving an output current signal as an input.