Abstract: The system for producing combustion ash of cellulose-containing wastes, provided with a kneading device 3 for kneading cellulose-containing wastes with a prescribed amount of liquid fuel oil, a molding device 5 for molding said kneaded mixture, and a combustion furnace 7 for burning said moldings, is characterized in that the humidity conditioning furnace 6 for adjusting the water content of said moldings is arranged between said molding device and said combustion furnace. Since the water content of said moldings is adjusted by the humidity conditioning furnace at the time of burning said moldings, the organic substances (cellulose or the like) are burned almost perfectly. Consequently, the present invention has the advantage of being able to produce combustion ash of good quality without generating such combustion residue as graphite and black smoke.