To effectively clean soil polluted with organic volatile chemical substances such as trichloroethylene or the like.

A large number of quick lime columns 5 are formed in polluted soil 1 to be treated a predetermined density and allowed to stand for a predetermined period and a pollutant is gasified by heat generation reaction generated by the contact of the quick lime columns with moisture in soil to be gradually diffused to the atmosphere in allowable concentration or less. After this method is adapted, quick lime having formed the quick lime columns and polluted soil are stirred and mixed to accelerate heat generation reaction to further gasify the pollutant to diffuse the same to the atmosphere. Quick lime is added to and mixed with polluted soil at the time of the mixing of polluted soil and quick lime under stirring.