PURPOSE: To reduce the ripple and to improve the responsiveness by giving a prescribed phase difference to four pulse width modulated wave trains with a phase shifting means, in the case a generating means generates four pulse width modulated wave trains.

CONSTITUTION: A phase shifting means 44 shifts a phase in accordance with the number of modulating parts 43 with respect to a triangular wave S1 from an oscillator 42, and gives a prescribed phase difference to each triangular wave S1. The modulating part 43 modulates pulse width by the voltage of an input signal S2 of an error amplifying part 48. A switching part 46 executes switching by the prescribed ON-duty. A driving signal S4 is subjected to phase- shifting at the time of rise in accordance with phase-shifting of a pulse width modulated wave train S3, and each pulse current signal S5 is also subjected to phase-shifting in accordance therewith. Each pulse current signal thereof S5 becomes a synthesized pulse current S7 and is outputted. In the pulse current S7, a ripple L getting on each pulse current signal S5 is superposed and ripples L0 whose height is low by four times are incorporated apparently.