To provide a system for treating contaminated soil capable of easily and inexpensively cleaning contaminated soil containing harmful materials while saving water used to a minimum necessary amount.

The system for treating contaminated soil 1 is provided with a first classifying means (a first oscillation screen 2) classifying treated soil S obtained by mixing contaminated soil with quick lime, a crushing means (a crushing device 3) crushing the treated soil of a predetermined particle size range which is classified by the first classifying means, a second classifying means (a second oscillation screen 4) classifying the treated soil crushed by the crushing means and a water washing means (a rock washer 5) washing by water the treated soil of a predetermined particle size range which is classified by the second classifying means.