To prevent acid gas and low boiling point heavy metal or the like from being circulated and condensed by a method wherein a dust collecting device at a melting furnace is installed at a molten discharged gas passage and there is provided a dust-removed discharged gas feeding passage for use in guiding the discharged gas with its dust being removed and processed by the dust collecting device at the incinerator and the discharged gas with its dust being removed and processed by the dust collecting device at the melting furnace toward an acid gas processing device.

An ignited discharged gas passage 6 of an incinerator 2 is provided with a waste heat boiler 8, a temperature reducing tower 9, a bag filter 10, an acid gas processing device 11, an induction blower 12 and a chimney 13. In this case, a discharged gas passage extending from the bag filter 10 to the acid gas processing device 11 is applied as a dust- removed discharged gas feeding passage 14. An incinerating, melting and processing facility 1 is provided with an incinerated ash transferring passage 15 for use in guiding ignition ash 4 from the incinerator 2 to the melting furnace 3 and further it has a flying ash transferring passage 16 for guiding flying ash 5 collected by the bag filter 10 to the melting furnace 3. The molten discharged gas passage 7 extending from the melting furnace 3 is provided with an air preheater 17, a gas cooling tower 18 and an electrical dust collector 19, wherein the molten discharged gas passage 7 is connected to the acid gas treatment device 11 through the dust removed discharged gas feeding passage 14.