The invention provides a technique to widely spread the frequency spectrum of switching noise generated by a switching action and to reduce the noise level at a particular frequency. A switching regulator (6A) includes a computing unit with computing function. First, in the computing unit, a pulse-width-modulation processing unit (PWM) (2a) performs pulse-width-modulation processing of receiving a feedback signal corresponding to the output of a detector 1 to determine an on-duty cycle of a pulse signal. Subsequently, for the signal and data obtained by the PWM (2a) to be subjected to further modulation processing for spectrum spreading, a branching processing is performed by making changing-over unit (2d) randomly select asynchronous-modulation processing unit (ASM) (2e) or pulse-position-modulation processing unit (PPM). When the PPM is selected, another branching processing is performed by making the changing-over unit (2d) select a first PPM (2f) or a second PPM (2g) depending on the on-duty cycle.