To reduce a running cost by using discharged soil in a high- temperature state.

Contaminants in the soil are gasified by a burner 11 in a rotary kiln 1, and the gasified contaminants are fed to a combustion furnace 19 to be burned and incinerated. The heated soil where the contaminants have been gasified and the above treatment has been completed is discharged to the outside of a discharge system 27 by a discharge gate 25 so as to be separated into a recycle system 29. After the heated soil and contaminated soil, which is newly heated, are preheated by an agitator 41 for circulation, they are fed to a charging hopper 7 in the rotary kiln 1.