To provide a waste treatment method facilitating the detoxification and effective utilization of the gas and residue from a combustion furnace by performing dechlorination as pretreatment.

Chlorine-containing waste is pyrolyzed and dechlorinated and alkali metals and a hydrocarbon decomposing catalyst are added to this treated waste to gasify and burn the same to perform detoxification treatment and, further, fly ash discharged from a combustion furnace 8 is heated to high temp. to be subjected to melt treatment. By this constitution, the amt. of the waste is still more reduced and, in the fly ash heating and melting treatment process, the molten matter after melting is stepwise cooled to separate and recover valuable metal.