and efficiently heat up the waste p as compared with direct heating operation by the flame f of the first burner 32 the molten residue p1 thus produced flows down along the common bottom wall 12 and is introduced into the second waste treatment chamber 40 similarly in the second burner chamber 50 the second burner 42 is previously ignited so that air in the second burner chamber 50 is heated to the high temperature the hot air thus heated flows into the second waste treatment chamber 40 through the side opening 40a the hot air further heats up the molten residue p1 introduced into the second waste treatment chamber 40 to a further extremely high temperature thus the molten residue p1 is completely melted to a final molten residue p2 the final molten residue p2 thus produced further flows down along the common bottom wall 12 and falls down into the cooling water c reserved in the cooling tank 70 through the outlet port 60a of the drop output chamber 60 the final molten residue p2 is cooled and cured by the cooling water c in the cooling tank 70 thereby producing solid residue p3 which may be easily handled and reused additionally when the molten residue p1 and the final molten residue p2 are produced in the.