To provide a method of increasing treatment in a gasification furnace capable of increasing a disposal amount of industrial waste in the gasification furnace while using conventional equipment and keeping a conventional supply amount of combustion air without changing the equipment of a gasification melting furnace by enriching oxygen, and increasing employment cost, electric power cost and the like.

In the gasification furnace 4 as a control target, shredder dust (raw material) charged to a fluidized bed 4a fluidized by oxygen mixture air is thermally decomposed in a temperature atmosphere of about 530°C to discharge incombustibles 7 and metal, and to discharge a generated nonflammable gas to a melting furnace of a subsequent stage. The air supplied to a supply opening 45 for fluidization and combustion air is the mixed air of the air in the atmosphere by a blower 50 and oxygen separately supplied from piping 51, and oxygen concentration of the mixed air is adjusted to 21.0-22.5% higher than an oxygen concentration 20.9% in the atmosphere.