To clean both of soil and stones.

Stones are separated from soil by a trommel 11 and the stones of specified size are discharged. Small stones other than the same and soil are introduced into a crushing mixer 18 and the crushing of soil and the mixing of treating agent are performed by means of the mixer 18. The soils admixed with the treating agent are charged into a thermal decomposition treating means 20, organic halogen compounds are decomposed, react with the added treating agent and generate harmless compounds. The treated material which is cleaned by the thermal treatment is guided to an intermittent discharging device 36 and, thereafter, is sent to a recovery means 50.