PURPOSE:To prevent a flow of gas when an overheating is found by a method wherein there are provided a valve and a valve seat which may stop the flow of gas by being contacted to each other and a low melting metal through which gas may freely be flowed is installed between the valve and the valve seat. CONSTITUTION:Safety device for preventing an overheating is stored in the burner 5 in reference to the fact that a temperature of the burner 5 is also increased as a temperature of the curled pipe 6 of in-pipe combustion device is increased. When the curled pipe 6 is overheated, a temperature of the burner 5 is also increased. If the temperature is higher than a melting point of the fuse metal 34, the fuse metal 34 is melted and then the valve 32 pushed down by the valve spring 31 is molten and adhered to the valve seat 33 to clog the gas passage and finally the combustion is terminated. Thereby, it is possible to provide a positive shut-off of the passage in the burner when the in-pipe combustion devide is overheated.