To quickly and accurately detect the temperature change of an object or substance being a temperature controlled subject and to avoid abnormal temperature fluctuation.

A gap between a heat receiving part 4a arranged to come into contact with or come close to the object being the temperature controlled subject and a bimetal 3 arranged to be opposed to the heat receiving part 4a is filled with high heat conductive substance 5 such as silicone grease. Thus, heat absorbed by the heat receiving part 4a from the object being the temperature controlled subject is quickly transmitted to the bimetal 3 through the substance 5. When the temperature of the bimetal 3 rises to a set value or more, the bimetal 3 is deformed to press a moving pin 6, and the movable side contact 9 of a leaf spring 7 is disconnected from a fixed side contact 8 in response to such pressing. Therefore, the responsiveness of the thermostat is remarkably improved and the abnormal temperature fluctuation is prevented.