PURPOSE: To provide a DC/DC converter having simplified circuitry.

CONSTITUTION: A comparator CP constituting a PWM control section compares a voltage V+ at a comparison input end +, where a feedback voltage at a comparison output end is superposed on a power supply side divided voltage, with a voltage V- at a comparison input end - where the integrated voltage of the comparison output end voltage VCP is applied. The comparator CP outputs a square wave voltage VCP having high level over the interval where the voltage V+ is higher than the voltage V-. A voltage based on the voltage VCP is smoothed by a capacitor C2 to produce an output voltage DCOUT on the load side. When the output voltage DCOUT increases, for example, a Zener diode ZD decreases the impedance of a transistor Q2 in reverse proportion to the difference of divided voltage on the load side from a set output voltage DCOUT. Consequently, the voltage V+ drops to decrease the increasing interval of integrated voltage thus decreasing the high level interval of the voltage VCP. The output voltage DCOUT is thereby dropped down to a set level.