According to the present invention, in the DC/DC converter having the capacity for driving a sWitch arranged betWeen an input poWer source and a load, the sWitch can be held ON Within a range Where the capacity is not discharged, so that a large duty can be obtained if the difference betWeen a supplied input voltage and an output voltage to be kept is
small, and the minimum value of the input voltage required for generating the output voltage to be held becomes smaller.