To provide a thermostat for keeping sealing case open, which is capable of remaining in an opening position after the thermostat is quickly moved to the opening position until power supplied to a device is cut off or removed.

A resistor 34 is mounted on a first end of a blade 20. The resistor is disposed between a cover plate 14 and the blade 20 in the closed interior of a case 12. The resistor 34 has a first side surface facing to and abutting on the cover plate 14 and a second side surface facing to and abutting on the blade 20 so that the cover plate 14 is electrically connected to the blade 20. The resistor 34 has sufficient resistance so that, when a second end of the blade 20 moves from a first position to a second opening position, a sufficient amount of heat is produced by a current flowing through the resistor 34 in order to keep the second end of the blade 20 at the second position until a load current supplied to the cover plate 14 and to the blade 20 is removed.