To provide a processing method for solid substance contaminated with dioxins which enable to decompose the dioxins in at atmospheric pressure and a relatively low temperature with simple equipment.

The processing method for the solid substance contaminated with the dioxins comprises reducing the solid substance containing the dioxins such as soil, bottom mud, incinerated ash, fly ash, and activated charcoal to not more than 20 meshes and reducing water ratio to not more than 20 wt% and then contacting it with sulfurous gas, and practically, gas containing the sulfurous gas of 1-100 volume % at 20-250°C. The sulfurous gas is formed by evaporation of liquefied sulfur dioxide and introduction of it into a sulfurous gas contact vessel, by putting of sulfite or hydrogensulfite salt together with the solid substance containing the dioxins into a sulfurous gas contact vessel to generate in the sulfurous gas contact vessel, and by use of the sulfurous gas in the exhaust gas generated in an incinerator or by other methods.