To provide a cost effective and efficiently treatment method which is capable of simultaneously lowering the concentration of the residual heavy meals and the heavy metal elution value of precipitate to an environmental reference value or below by subjecting a slurry containing soil contaminated with heavy meals, such as lead, to simultaneous treatment with subjecting the same to a separation of solid from the liquid.

The slurry prepared by inclusion and coprecipitation of the heavy metals by the hydroxide by adding a mineral acid to the slurry containing the soil contaminated with the heavy meals, such as lead, to adjust its pH within 2 to 4, adding 0.1 to 5.0 g/L iron salt as iron to the slurry and stirring the slurry, then adding an alkali thereto to adjust the pH within a range from 7 to 10 is subjected to the separation of solid from the liquid, by which the slurry is classified to the precipitate and treated waste water. The lowering of the concentration of the residual lead in the treated waste water and the lead elution value in the insolubilized soil simultaneously to the environmental reference value or blow is made possible by this method.