PURPOSE: To know the degree of wear of the surface of grain and to control the grain properly in accordance with the degree of the wear of the surface.

CONSTITUTION: Grain received by a receiving hopper 1 is supplied to a weighing unit 4 via an elevator 2 for reception and a rougher 3. The weighing unit 4 weighs the received grain and also extracts a part of it as a measuring sample. A surface wear detecting device 6 subjects the sample to a dehusking process to make it unmilled rice and detects wear of a surface showing the degree of breakdown of a rice bran layer of the surface of the unmilled rice. In accordance with the result of detection, the grain being weighed by the weighing unit 4 currently is sent into prescribed sorting tanks 10A to 10D by a sorting conveyor 9.