PURPOSE: To impart compression force and shearing force to a raw material to be ground and to enhance grinding efficiency by forming at least one of a pair of left and right rolls into a truncated cone shape.

CONSTITUTION: The raw material freely falling from the discharge port of a hopper is supplied to a pair of rolls 3,4 rotating around horizontal shafts. A pair of left and right bearings 3a supporting the rotary shaft of one roll is fixed and a pair of left and right bearings 4a supporting the rotary shaft of the other roll are arranged in a slidable manner in the direction right-angled to the shaft, and hydraulic cylinders 5 are connected to the bearings 3a to compress and grind the aforementioned raw material to be ground between the peripheral surfaces close to each other of the rolls 3, 4. At least one roll 3 among a pair of the rolls 3, 4 is formed into a truncated cone shape wherein the outer diameter of the roll gradually expands in the axial direction. As a result, compression force and shearing force can be imparted to the raw material to be ground and grinding efficiency can be enhanced.