To provide a contaminated soil treatment system which easily and inexpensively cleans contaminated soil containing harmful substances without using water, and can reuse the cleaned soil, and a treating method.

The treatment system 1 is provided with a mixing means (mixing device 2) mixing the contaminated soil with unslaked lime to obtain treated soil; a first classifying means (first vibration screen 3) classifying the treated soil obtained in the mixing means; a crushing means (crushing device 4) crushing the treated soil in the give range of particle sizes classified by the first classifying means; and a second classifying means (second vibration screen 5). The mixing means and crushing means share the same apparatus.