To provide a sawtooth wave generating circuit which is simple in configuration, capable of generating accurate sawtooth waves, and obtaining the good linearity of an outputted duty ratio even when the sawtooth waves are used as a comparison waveform of a PWM comparator in a DC-DC converter of a PWM method.

The sawtooth wave generating circuit is equipped with an operational amplifier Q1, a voltage comparator Q2 which compares the output voltage of the operational amplifier Q1 with a set voltage, a capacitor C1 which is connected between the output terminal and inverted input terminal of the operational amplifier Q1, a switch SW1 which is connected to the capacitor C1 in parallel and turned ON or OFF by the output of the voltage comparator Q2, a first current source I1 connected to the inverted input terminal of the voltage comparator Q2, and a second current source I2 connected to the output terminal of the operational amplifier Q1. The operational amplifier Q1 is formed of a single-stage differential amplifier circuit.