To enable to make dioxins harmless at a lower cost by using coal ash as a treatment agent effectively, which has a treatment temperature lower than the boiling point of water, and is disposed as industrial wastes and utilized as landfill in a large volume.

Ash containing dioxins is fed to a solid-liquid contact device 10 whose temperature is maintained lower than 100°C through a line 11. The ash is brought into contact with coal ash in the solid-liquid contact device 10 to which a hydrochloric acidic solution is fed through a line 13. Gas (exhaust gas) after contact with the solution is exhausted from a line 103. The treated ash and coal ash after the solid-liquid contact are fed to a solid-liquid separation device 2 from a line 15, and the solid is separated from the liquid. The solution after separation is fed to a metal separation device 3 from a lien 16, and the separated metal is fed to a copper separation device 4 from a line 19 to separate copper ion in the metal.