PURPOSE: To efficiently grind various matters to be ground such as industrial waste, large size waste refuse or the like.

CONSTITUTION: A high speed main cutter 3a and a low speed sub-cutter 3b are combined and the blades 4b of the sub-cutter 3b are attached in an opposite direction with respect to a rotary direction. A first feed roll 7a is provided so as to approach the intermediate part between the cutters 3a, 3b from above and a second feed roll 7b is provided in close vicinity to the feed roll 7a and the sub-cutter 3b. Further, the feed roll 7a is pressed to the feed roll 7b under definite pressure by a hydraulic cylinder 9a. By this constitution, even large size waste refuse such as a futon, mattress or a refrigerator can efficiently be ground.