PURPOSE: To realzie a temperature sensor with a high detecting accuracy by using a quarts oscillator and dampers arranged close to both of the two opposite surfaces of the quartz oscillator.

CONSTITUTION: Dampers 3 are arranged so as to sandwich both the tow opposite surfaces of a quartz oscillator 1 and to be close to the surfaces and a quartz oscillator circuit is connected to the quartz oscillator 1. Below a detecting temperature, gaps between the quartz oscillator 1 and the dampers 3 are maintained and the oscillator 1 oscillates to let the quartz oscillator circuit produce an output. When the detecting temperature is reached, the quartz oscillator 1 and the dampers 3 are brought into contact with each other and the oscillation of the quartz oscillator 1 is damped, resulting in the stop of the oscillation of the oscillation, it can be accurately detected that the detecting temperature is reached.