To provide a cleaning method of contaminated soil capable of easily and positively insolubilizing and immobilizing contaminated soil contaminated by dioxin, heavy metals, or the like at a present location without scattering it.

The cleaning method of the contaminated soil includes the steps of: partitioning the entire or a part of a partition of contaminated soil with an outside air shielding partition object, excavating the contaminated soil inside thereof to be granulated into a predetermined particle size, mixing a siloxane and silanol salt multimolecular solution with this granulated contaminated soil in the ratio of 5 to 15 wt.% to be kneaded, approximately evenly mixing and adhering the multimolecular solution on the whole outer surface, applying heating treatment at 600 degrees or higher to achieve insolubilization and immobilization, and re-filling it in an excavation site.