PURPOSE: To easily remove the refuse held between a detecting unit and the gutter of a shoot while grains flow down, by making the detecting unit removable in position.

CONSTITUTION: Grains dropping from a hopper 2 into a reservoir member 3 enter supplying conduit 5 one by one along a guide board 4 and flow down onto the gutter 9 of a shoot 8. A light is applied to the grains by a light source 11 and a lens 13a through a slit 10, and cracks of the grains are detected by the lens 13b of a detecting unit 12 and the fiber scopes 14a and 14b thereof and by detectors 15a and 15b and recorded in a counter 16. When refuse is held between the detecting unit 12 and the gutter 9 of the shoot 8, the detecting unit 12 is rotated upward around a rotary shaft 19 by lowering a lever 20. A cover 24 is opened, the refuse is removed through a window 23, the cover 24 is closed after completion of removal, and the lever 20 is lifted up to a position where it touches a stopper 22. Thereby the detecting unit 12 returns again to an adjusted position.