To provide a technology which purifies and recycles not only coarse-grained soil but also fine-grained soil by directly passing suspended water containing fine-grained soil classified by soil washing and dioxins through a compact photocatalytic device to oxidatively oxidize and detoxify the dioxins.

Contaminated soil 25 is immersed and left in an aqueous solution containing a cleaning agent, such as a surfactant 27, in a temporary tank 26. The contaminated soil 25 is washed in a first washing device 28. The contaminated soil 25 is carried into a temporary tank 29 to be stirred for a fixed time. The supernatant wastewater 30 is sent to a water storage tank 31, and the contaminated soil 25 is rinsed in a second washing device 32. Subsequently the contaminated soil 25 is classified in a vibrating screen classifier 34. The photocatalytic device 39 oxidatively decomposes and detoxifies dioxins (DXNs) adhering to fine-grained soil 36 and organic matter.