Provided next is the explanation about the operations after the latch circuit 5 is set by the pulse (hereinafter referred to as a set pulse) output from the oscillator 2 at a time T0, Which leads to the transition of the sWitch S1 from the OFF to the ON state. The oscillation frequency of the oscillator 2 is, for example, on the order of several hundreds of kHZ. In this case, the set pulse is generated every several p seconds. Note that this frequency is the fundamental sWitching frequency of the DC/DC converter.