To make excavated soil suitable for backfilling not only when the excavated soil is solid but also when the excavated soil is construction sludge.

A 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. The treatment part D includes a treatment side conveying part 3 receiving the excavated soil from the supply side conveying part 2 and receiving treatment materials discharged from the treatment material feeder T to convey them to the downstream side, and a mixing device 4 disposed behind the treatment side conveying part 3 to mix the excavated soil discharged from the treatment side conveying part 3 and the treatment materials together. The supply part S and the treatment part D are connected together in series and disposed horizontally, while a gate mechanism 6 regulating a passing amount of the excavated soil is arranged in the boundary between the supply side conveying part 2 and the treatment side conveying part 3.