PURPOSE: To prevent the generation of burning irregularity or burning blocks making the sectional area of a combustion chamber larger than that of a preheating chamber, and provid ing a smoothing columnar member, the upper end of which is formed into a conical shape, from the inside of a cooling chamber to the lower part of the combustion chamber concentrical ly with a main burner body.

CONSTITUTION: The sectional area of a combustion chamber 5 is made larger than that of a preheating chamber 4. The moving speed of a material 3 to be burned within the combustion chamber 5 is made slower than that within the preheating chamber 4, and hence it is possible to obtain a staying time required for completely conducting self-sustained combustion up to the center of the combustion chamber 5. A smoothing columnar member 11 having an upper end of a conical shape, produced a mutual friction movement due to an interaction of an action to move along an inclined surface and that in the vertical direction thereby to sufficiently carry out mixing and agitating of the material 3 to be burned. By using a rotating scraping bar 13, coupled with the operation of the smooth columnar member 11, the flow of the burned material is smoothed, and this contributes to the irregular burning preventive operation. Air flows sufficiently in the vicinity of the wall surface, and hence combustion of the material 3 to be burned in the vicinity of the wall surface can be sufficiently carried out.