To efficiently and economically remedy soil polluted with harmful substances within a short time by surrounding the polluted soil with water shielding walls such as continuous underground walls and repeatedly elevating and lowering the water level of underground water with a remedying solution by repeatedly pouring the remedying solution into the objective soil surrounded with the water shielding walls and discharging the solution.

After water shielding walls 1 and wells 4, 5 for pouring water and pumping up water, respectively, are installed, water is pumped up through a pumping up well 5. Since the objective soil 3 to be treated is surrounded with the water shielding walls 1, the water level of underground water is continuously lowered to the position lower than the depth of the polluted soil by pumping up water. Then, pumping up is stopped and after that water or a treatment solution produced by adding necessary chemical agents to the water is poured through the water pouring well 4, so that the water level of underground water is increased to dampen the polluted soil with the treatment solution. Lowering of the water level of underground water by pumping up water and dampening of the soil with the treatment solution by pouring the solution are properly repeated in such a manner to carry out remedying treatment and the soil is easily dampened and the treatment solution and the objective soil to be treated can efficiently be brought into contact with each other to complete remediation treatment within a short time.