To provide a method for subjecting excavated surplus soil/sludge to separation treatment by soil quality and a device therefor in which excavated surplus soil or sludge having large clay lumps can be directly treated without using a surplus soil pretreatment means even when there are large clay lumps.

Excavated surplus soil/sludge containing clay lumps D in which clay or the like and sand or the like D2 coexist are fed to a rotary perforated plate 1 to raise the clay lumps D to a high position of the rotary perforated plate 1 by the rotation of the rotary perforated plate 1 and to make it fall to a pulverizing means F installed in the rotary perforated plate 1 and consisting of a rotary brush body 5 and a pulverizing plate 11 abutted on the peripheral surface thereof, and they are pulverized between the rotary brush body 5 and the pulverizing plate 11, and furthermore, water is sprayed to them to subject clay or the like to forced filtration and to separate clay or the like from sand or the like D2.