To provide a grinder which can properly perform the grinding process and the classification process, even in case the rotating rate of a grinding rotor is increased for upgrading the throughput capacity, and thus can certainly improve the throughput capacity.

This grinder has the following configuration: (1) the grinding rotor 4 which rotates around a longitudinal axis and a gas introduction port 2, arranged at the internal lower part of an upright barrel-type processing chamber 3, (2) a classification part 5 and a discharge port 12 which discharges a classification powder of a specified grain size classified, arranged at the internal top of the processing chamber 3, (3) a concentric cylindrical member 6 arranged to the rotary shaft of the grinding rotor 4, between the grinding rotor 4 and the classification part 6, (4) a lower side annular part 6A with a lower surface extending externally toward a grinding part 4A of the grinding rotor 4, arranged at the lower end part of the cylindrical member 6, and (5) a sheet-like member 11 with a sheet surface extending longitudinally toward the interior of the processing chamber 3, arranged on the inner wall side of the processing chamber 3 opposed to the upper side part of the cylindrical member 6.