To permit combustion and melting of sludge with one stage of treatment, by a method wherein dried swage, sludge, or the like is transported by air stream to blow the same into a melting furnace to produce high-temperature reduced gas through partial combustion of organic matter in the sludge and, simultaneously, melt inorganic matter in the sludge to recover slag type solid matter.

Upon transporting dried sludge into a melting furnace 3 by air stream when the sludge generated by the disposal of sewage through incineration is disposed, the sludge is gasified by blowing the dried sludge and oxygen or oxygen-enriched air by a burner 8, then, the dried sludge is guided out of the melting furnace 3 into a cooling furnace 4. In this case, the molten particulate slag is collided against the side wall of the molting furnace 3 to liquefy the same and drop the same from a slag discharging port 10 into a water pot 11 to cool the same and, thereafter, the same is discharged after being solidified. Produced gas is cooled in the cooling furnace 4 and, thereafter, the same gas is allowed to cool and solidifies molten slag, accompanied by gas from the melting furnace 3. Thereafter, slag in the cooled gas is removed by a cyclone 5 and the heat of the cooled gas is recovered by a boiler 6 while the slag is removed again by a dust collector 7.