To provide a method and a device for treating chlorine compounds in incineration ash, by which unburned substrates such as dioxins or dioxin precursors contained in the incineration ash, incineration fly ash or the like are highly decomposed.

Organic chlorine compounds such as unburned substances being dioxins and dioxin precursors adsorbed on or contained in the incineration ash, incineration fly ash or the like are decomposed in a molten salt (reactor) composed of two or more alkaline metal carbonates selected from sodium carbonate, potassium carbonate and lithium carbonate and one or more alkali nitrates selected from sodium nitrate, potassium nitrate and lithium nitrate, and then the molten salt is removed from the incineration ash or the incineration fly ash by washing (by shower).