To operate it surely at a set temperature, by offsetting the dispersion of voltage between a base and an emitter in manufacture process of a transistor which serves as a temperature sensor, in a thermal shut down circuit.

In the case of making the voltage between the base and the emitter of a transistor Q1 a temperature sensor, reference voltage obtained by two resistors R1 and R2 is added to the base of a transistor Q. A constant voltage source 4 outputs the voltage having the positive-negative reverse dependency upon temperature to the dependency upon temperature of the voltage between the base and emitter of the transistor Q1. An emitter follower circuit 20 lets a current flow, based on the output voltage of the constant voltage source 4, and this current has not dependency upon temperature, but it ripples according to the dispersion of the voltage between the base and the emitter of the transistor Q2. A current at roughly the same value as this current is drawn out of the base of the transistor Q1 by two current mirror circuits 30 and 40.