PROBLEM TO BE SOLVED: To effectively perform decontamination without generating polluted water when treating the contaminated soil.SOLUTION: A method for treating contaminated soil is configured such that: a soil collected in contaminated soil collecting step (S100) is dried in a drying step (S110), and further, a dried soil aggregation is loosened in a crushing step (S120) so as to adjust the particle size of the dried soil to a particle size suitable for separating soil according to the particle size in a subsequent classifying step (S130). Accordingly, the generation of a variation in classification accuracy caused by the conditions of soil to be treated, such as the water content or the aggregation of the collected soil is avoided and as a result, the classification accuracy is enhanced. Additionally, the soil with a small particle size, of the soil separated in the classifying step, is isolated (S150) in a subsequent managing step (S140), and the residual soil is returned back to a soil collecting place
