PURPOSE: To carry out the heating of the inside of a furnace and generate an environmental gas for protection.

CONSTITUTION: A tube 3 that forms a cylindrical combustion chamber which has a diameter smaller than that of a radiant tube 2 and opens at both ends is arranged in the radiant tube 2 that is cylindrical and has a bottom. The openings at one end of the radiant tube 2 and at one end of the tube 3 for forming combustion chamber are closed by a closing member 8. A burner 9 is arranged in the tube 3 for forming combustion chamber and is attached to the closing member 8. At the other end section of the tube 3 for forming combustion chamber a port is formed which connects the inside to outside of the tube 3 for forming combustion chamber. A catalyst 6 is filled in between both tubes 2 and 3. A combustion gas outlet 8a that discharges the combustion gas coming through the catalyst 6 is formed in the closing member 8. A radiant tube 2 is used by attaching it to a furnace F for defatting by heating so as to position the tube 2 in the furnace F.