To reduce the slide resistance of a radiant tube on the bung side by supporting a burner or a recuperater main body through a rotating body on the furnace shell protruding side of a radiant tube of a heat treatment furnace, and combining the section going through the furnace wall of the burner or the recuperater with a flexible combining body.

A resistance is eliminated by adopting a flexible combining body (bellows made of fabric) 4, and in order to reduce the deforming resistance of a connecting tube, the connecting tube is replaced by a flexible tube 5, and the resistance is reduced. For a rotating body (rolling body) 8 between a burner support 6 and a bearing fitting 7 on the bung side, a cylindrical roller is used. For the rolling body 8, article other than the cylindrical roller may be used as long as the slide resistance of which is small, and which can perform a positioning. Since the rolling body 8 is attached to the outside of a burner 82, the environmental condition is comparatively favorable. Even when a seizure occurs on a radiant tube support 11, a radiant tube 1 can freely extend to a burner 2 side. Therefore, a thermal stress is softened, a bending deformation is reduced, and life can be extended.