PURPOSE: To prevent heat insulating material from falling down and elongate the life of a furnace by a method wherein at least one part of the heat insulating material, laid on the inner wall of the outer plate of a furnace main body, is supported by bolts, whose shafts are fixed orthogonally to the inner surface of the outer plate.

CONSTITUTION: An incinerating furnace is provided with a rectangular shape and refractories 4 on the furnace walls 5 of peripheral four surfaces are fixed by bolts 3 while the refractories 4 on the ceiling of the same are constructed so as to have the shape of an arch in the manner same as so far. The refractories 4 are fixed to the inner surface of the furnace wall 5 through bolts 3 at every three pieces of the refractories 4 in respective stages while the ends of the bolts 3 are welded orthogonally to the outer plate 2 of the furnace. The refractories 4 are fitted between the heads of the bolts 3 and the outer plate 2 of the furnace and are piled up while fixing them sequentially by mortar 11. According to this method, the falling down of the heat insulating material may be prevented and, therefore, the outer plate of the furnace will never be exposed to high heat whereby the life of the furnace may be elongated.