To provide a method for improving contaminated soil which can easily carry out continuous purification of contaminated soil at a low cost over a long period of time.

Cylinders 3 having water passage holes 2 are embedded in the ground 1 where the soil has been contaminated. An adsorbent 4 is housed in the cylinder 3 so as to be freely put in and out of the cylinder 3. Contaminants contained in groundwater infiltrating into the cylinder 3 through the water passage holes 2 are adsorbed by the adsorbent 4. The adsorbent 4 having adsorbed the contaminants is collected on the ground, and then the new adsorbent 4 is put into the cylinder 3. These operations are repeated to improve the contaminated soil.