To remove dust effectively from a combustion exhaust gas from a combustion melting furnace which burns waste and so forth and prevent corrosion or troubles, thereby enhancing maintenance or operation efficiency.

A combustible matter 11 such as waste and a combustion air 12 are supplied to a combustion melting furnace 10 for combustion. A combustion exhaust gas 14 which is produced with molten slugs 13 is supplied to a waste heat boiler 17 in the rear stage of a high temperature air heater 15. A cyclone 18 is provided by the application of an evaporation zone in the front stage of the waste heat boiler 17. A refrigerant tube is laid out on the outer peripheral surface so as to provide a function as a radiant room. Due to this construction, dust is removed at the cyclone and the combustion exhaust gas, whose temperature is dropped, generates steam 22 at the waste heat boiler. Then, the steam is supplied to equipment, such as a temperature reducing tower or an exhaust gas filter device, which makes it possible to separate and remove the dust preliminary and effectively, and drop the temperature of the high temperature combustion exhaust gas to a specified range so high temperature corrosion can be prevented, and reduce dust-imposed load for exhaust gas treatment equipment in the rear stage.