Still further, in the above described preferred embodiment, the con?guration Where the output voltage of the DC/DC converter is controlled by a PWM. HoWever, the present invention may be applied to the con?guration Where the output voltage is controlled by a PFM. For the con?gu ration controlled by the PFM, the oscillator 2 and the ramp signal generating circuit 3 are not required in FIG. 4, and the output of the comparator 12 is input to a one-shot off time circuit, Which holds the sWitch S1 in the OFF state during a predetermined time period upon receipt of the reset pulse from the comparator 12.