PURPOSE: To improve thermal efficiency and reduce troubles by a method wherein the inserting ports of works to be heated are provided radially and a supporting device, supporting radiation burners, is provided with the supplying section of the works and a pushing rod while the operating means of the pushing rod and the driving means of rotation of the furnace main body are provided.

CONSTITUTION: A furnace main body 1, constituted of the heating chamber of a flat space in a tubular furnace, is supported rotatably by a supporting device 8, the furnace wall of the furnace main body 1 is provided with a burner setting port 2 at the upper central part of the same and the dropping port 4 of the works to be beated at the central part of the bottom while the sending ports 5 of the works 3 to be heated, which constitutes a preheating unit, are provided radially. A radiation burner 14, engaged with the burner setting port 2, is supported by the supporting device 8, the supplying unit of the works 3 to be heated and pushing rods 21, 22 for the works 3 are provided at positions opposing to the sending ports 5 of the supporting device 8 while the operating means of the pushing rods 21, 22 and the driving means of the rotation of the furnace main body 1 are provided on the supporting device 8.