To provide a soil treatment structure capable of improving properties of excavated soil to make them suitable for backfilling in either case when the excavated soil is solid or sludge.

The soil treatment structure includes a supply part S receiving the excavated soil, a treatment part D treating the excavated soil fed from the supply part S and discharging it outside, and a treatment material feeder T supplying treatment materials to the supply part D. The supply part S includes a hopper 1 receiving the excavated soil, and a supply side conveying part 2 receiving the excavated soil discharged from the hopper 1 to convey it to the treatment part D. A seal member preventing leakage of the excavated soil is disposed between the supply side conveying part 2 on the upstream side of a gate mechanism 6 and the hopper 1.