To provide a thermostat operative at relatively high temperatures when the temperature of a fixer steeply rises and operative at relatively low temperatures when the temperature of the fixer slowly rises, and to provide a fixing device for an electrophotographic device.

This thermostat has a structure made by sandwiching a substance of low thermal conductivity between a first bimetallic strip and a second bimetallic strip. The first and second bimetallic strips are characterized by being disposed so as to curve to the same direction in response to a temperature change. This constitution potentiates the prevention of malfunction caused by abnormal detection of temperature.