PURPOSE: To facilitate the assembly into an integrated circuit by arranging the second power source so as to change in the output voltage thereof according to the output level of a voltage comparator corresponding to the first power source to make it as circuit easy to be a monolithic structure.

CONSTITUTION: As the forward voltage VF of diodes D1 and D2 has a negative temperature coefficient, the base potential VT of a transistor Q1 goes up with a rise in the temperature. On the other hand, the base potential VRT of a transistor Q2 becomes constant with respect to temperature change. A latch circuit 7 composed of a voltage comparator 2 and a power source 3 acts as a temperature detection circuit with the transistor Q2 conducting while the transistor Q1 is shut down. Then, a control circuit 4 is added to control the latch circuit 7 to the initial state. As the junction temperature Tj rises to reach the detection temperature Tc, VT-VRT0 is given and the potential VRT falls causing the transistor Q1 to conduct so suddenly that the transistor Q2 is shut down to bring the output terminal 6 up to a high level, thus indicating that it is beyond the detection temperature Tc.