PURPOSE: To prevent intrusion of very fine powder of a crushed matter between crushing rolls and a casing.

CONSTITUTION: A crushing device is provided with upper crushing rollers 3 and 4 forming a couple in parallel and a lower crushing roller 5 positioned below the upper crushing rollers, and screw-shaped crushing plates are mounted on respective crushing rollers, and crushing is carried out by a couple of upper crushing rollers 3 and 4. The crushing is carried out again by the lower crushing roller 5 and either one of the upper crushing rollers, and crushed matters are discharged downward. Flanges 6, 7 and 8 of almost same diameter as crushing plates are disposed protrudingly on both end sides to prevent the intrusion of crushed matters between the rollers and the side wall of a casing 2. Dustproof covers 20 covering the flanges 6, 7 and 8 are installed on the side wall of the casing 2 with very fine spaces allowing the rotation of flanges. The dustproof covers 20, therefore, prevent the intrusion of crushed matters into the spaces between the flanges 6 and 7 and the casing 2 and also prevent the trouble caused by the intrusion of crushed matters and dust into bearing sections.