To improve crushing efficiency and to increase crushing volume per unit time in particular.

Two crushing relationships are given among three rolls 1, 2, 3. The first crushing, or rough crushing, is done between the first and second rolls 1, 2, and the second crushing, or fine crushing, is done between the second and third rolls 2, 3. Crushing efficiency is improved by implementing the rough crushing and the fine rushing continuously. The crushing blades 12 of the first roll 1 are longer than the crushing blades 22, 23 of the second and third rolls 2, 3. The rotational radii of the outermost ends of the crushing blades 12, 22, 32 are combined appropriately in order to improve the crushing efficiency of the rough crushing and the fine crushing.