To provide a PWM signal generating circuit which employs as small number of components as possible and is which a required volume for final circuit mounting is remarkably reduced.

A DC/DC conversion circuit 10 is a circuit widely spread as a conventional integrated circuit and generates a comparison output signal (a) and a minimum conduction width signal (d) in its inside. An AND circuit 27 synthesizes both the signals, respective output terminals of AND circuits 32, 33 existing at the post-stage of the AND circuit 27 are connected to an inverting circuit 21 respectively via switch circuits 34, 35, an output of the circuit 21 is given to a waveform synthesis circuit 12, which synthesizes the output with a maximum conduction width signal (e) under the control of the signal (e) and provides an output of the result as an output signal OUT.