To solve the problem in the conventional art that dioxin is formed in incineration treatment of waste, and the dioxin is contained, as a natural result, in the incineration ash of the waste, if the ash is dumped as it is in a disposal site, the dioxin remains toxic, further if the dioxin is solidified with cement at normal temperature, hazard of the dioxin remains exposed.

In the treatment of general and industrial wastes, and treatment of incineration ash and fly ash, a system of a direct melting furnace is employed. The furnace comprises a coke bed, which is very effective for restriction of dioxin formation. In this furnace, a reduction reaction occurs at a temperature of at least 1,000°C, a sufficient temperature for conducting a thermal decomposition of dioxin. Slag melted at high temperature is discharged to the outside of the furnace and cooled, even if dioxin recombination is generated in the cooling time, elution of harmful mater is hindered by the sticking action of the slag.