PURPOSE: To quickly cut a low melting point fusible metal wire fused under a less flux amount by using, as a metal plate having an insulating film on one surface, an aluminum plate one surface of which is subjected to alumite treatment.

CONSTITUTION: When a shell plate part 93 is bored due to corrosion, a combustion gas is blown out from the hole, and the blown gas makes contact with a heat shielding plate 98, the heat is transmitted to a flat thermal fuse A with the contact position as the center. A low melting point fusible metal wire 6 starts fusing from the part closest to the combustion gas contact part, and the gas supplying solenoid vale of a gas burner 91 is closed by the cut of the fused metal to stop combustion. In this case, since the wire 6 makes contact with the oxide film of an aluminum plate 1 one surface of which is subjected to alumite treatment, the fused metal is sphered by the fusion of the wire 6, a fused flux 5 is bitten between the spheres, and the fusion of the fused metal can be quickly performed.