To effectively utilize natural aggregate resources by effectively recovering sand of good quality usable as concrete aggregate from natural sand.

Raw sand is fed into a hopper 1, and the raw sand discharged from the hopper 1 is conveyed by a conveying device to feed it to a classifier 4. In the classifier 4, the raw sand is washed with water and also is classified into a large diameter component, a medium diameter component, and a small diameter component. The small diameter component is fed to a pulverizer 5 together with water to pulverize viscous lumps or the like in the raw material, and next, the small diameter component is fed to an impurity removing device 6 as it is, and lightweight impurities such as chips of wood in the raw material are floated on the water to remove them, and the raw material from which the lightweight impurities have been removed are fed to classifiers 7, 8, 9, 10, 11 to classify them into fine sand and coarse sand, which are taken out.