PURPOSE: To sense a fire in a wide place by one sensor and apply the sensor even to a narrow place by providing a heat pipe, starting at a bimetal, almost horizontally.

CONSTITUTION: The bimetal 3 is arranged at the tip of a heat reception plate 2 and so constituted that when specific temperature is reached, an electric circuit 4 is closed to sound a fire signal. Then heat pipes 51 and 52 are formed by using mesh wicks for copper pipes and charging water; and their end parts are fitted in contact with the bimetal 3 and the other ends are arranged extending lengthwise almost in the horizontal direction. In this case, any part of the heat pipes 51 and 52 which extend to the right and left serve as a heat sense part and, for example, if heat is generated at the tip part of the heat pipe 52, this heat is conducted to the bimetal 3 at the sensor part momentarily by the vaporization of the working liquid in the heat pipe 52; and then the electric circuit 4 is closed through the operation of the bimetal 3 to send the fire signal.