To prolong the service life of a combustion tube heater used in a state where the heater is dipped in a molten metal held in a molten metal holding furnace and, at the same time, to improve the thermal efficiency of the heater.

This combustion tube heater is constituted in a triple structure of an inner tube 2, an intermediate tube 3, and an outer tube 4 and the inner tube 2 is constituted in such a way that its front end 5 is opened and rear end is connected with a fuel gas supply pipe 6 and an air supply pipe 7. The outer periphery of the inner tube 2 is covered with the intermediate tube 3 having a closed front end and the outer periphery of the tube 3 is covered with the outer tube 4 formed of a dense ceramic and having a closed front end. In addition, the space between the intermediate and outer tubes 3 and 4 is filled up with an air-permeable heat conductive material 10.