To provide a waste treatment system which, in general waste or industrial waste, gasifies waste to be gasified, and melts all waste not to be gasified, and recovers the waste as reusable solids.

A furnace of vertical type, shaft type, or crucible type is used. The inside of the furnace is made a high temperature of 1,000°C or higher, and is filled with a carbon solid heat source such as coke to be made a reduced gas atmosphere. Lead oxide, cadmium oxide, copper oxide, or other metal oxides in slag are reduced to be separated from the slag as a molten material of metal, so that the slag is reused as a pollution-free safe resource. When the waste is charged in the furnace, the composition ratio of CaO, SiO2, MgO, and Al2O3 which are components of the slag is calculated/estimated, the basicity of these slag composition, i.e. CaO/SiO2, (CaO+MgO)/(SiO2+Al2O3), is maintained in the range of 0.15 to 1.45, thereby the slag is made to be easily melted.