Abstract: A thermostat including a heater without a positive temperature characteristic thermistor or an alumina substrate. The thermostat with a filmy heater includes two terminals (2a, 3a) to be connected with an external circuit, a fixed plate (2) connected with one of said terminals and on which a static contact point (2b) is mounted, a resilient plate (3) connected with the other of the two terminals and on which a movable contact point (3b) is mounted, a bimetal (5) which is so deformed, when temperature of the bimetal exceeds a predetermined temperature, to deform the resilient plate so that the movable contact point is separated from the static contact point, and heater (6) mounted in parallel with said fixed plate and the resilient plate. The heater is an electro-conductive film (6a) on an insulative film (6b), which is incorporated in the thermostat.