To effectively utilize sensible heat of exhaust gas and achieve decomposition of organic chlorine compound such as dioxin securely irrespective of use of simple facility.

A ceramic filter 2 holding catalyst is provided in an exhaust gas flue at an outlet of an incinerator 1 or an outlet of a melting furnace to decompose organic chlorine compound in exhaust gas by dust removed from the exhaust gas and the catalyst in a temperature zone of 400°C or more. Scattered ash caught by the ceramic filter 2 is supplied into an external heat kiln type scattering ash treatment device 5 to heat it at temperature of 300°C or more in order to decompose dioxin by heat. Sensible heat of exhaust gas at an outlet of the ceramic filter 2 is utilized as its heat source. The exhaust gas at the outlet of the ceramic filter 2, inside exhaust gas from the inside of the scattering ash treatment device 5, and exhaust gas for external heat utilized as heat source are radiated into the atmosphere.