PURPOSE: To eliminate discharging of treated water at all and decrease the amt. of makeup water by evaporating the total amt. of the balance of the treated water to be recirculated to an incineration furnace and a scrubber in a gas cooler.

CONSTITUTION: The waste gas 6 produced by the incineration of refuse 5 in an incineration furnace 1 is flowed into a gas cooler 12. On the other hand, part of the treated water 10 of a waste water treating device 3 is brought in direct contact with a gas 6 as cooling water 10c to cool the gas 6, and to evaporate the entire amt. of the water 10c. The produced steam is flowed together with an outlet gas 6' to a scrubber 2, where salts 13 in the water 10c are separated as solids. The gas 6' is scrubbed by the scrubbing water 5 which is the mixture of the other part 10b of the water 10 and makeup water 11, by which it is removed of harmful components, dust, etc. to make a treated gas 7. Part of the water 4 evaporates but the other part is waste water 9 which is flowed into a device 3. The waste water 8 of ash removal of the furnace 1 is treated with the device 3 and is used as water 10a for ash removal.