Abstract: An apparatus for preventing the emission of dioxins in an incineration facility including an incinerator having a boiler, and an exhaust gas treatment facility for treating exhaust gas discharged from a flue of the boiler. This apparatus further includes a steam supply pipe for supplying steam into a water tube or a downcomer of the boiler from an auxiliary boiler or another steam-generating source, a flue damper for opening and closing the flue of the boiler, a detector for detecting the temperature of gas within the boiler at a point disposed upstream of the flue damper, and a damper control device responsive to a temperature, detected by the detector, for opening and closing the flue damper.