PURPOSE: To prevent the mixing of a coarse powder with a fine powder in a final classifying stage to the utmost by making the height of a cylinder vertically suspended around a fine powder discharge port controlling tertiary classification variable to set the height of the cylinder so as to obtain the optimum tertiary classification and discharging the coarse powder excluded by the tertiary classification from the through-hole of a rotary impeller.

CONSTITUTION: A rotary impeller 8A wherein a plurality of rotary blades 8 are provided to the periphery of a drive shaft 8 is arranged within a fixed blade 6 and a fine powder discharge port 9 is provided directly above the rotary impeller 8A. A cylindrical slide gate 20 freely movable up and down is provided to the lower part of the fine powder discharge port 9 and the rotary impeller 8A is formed as a conical disc having a stepped part and through-holes 80 discharging a coarse powder are provided to the stepped part. As a result, a classicying point is more transferred toward a fine powder side and the mixing of the coarse powder with a fine powder in a final classifying stage is prevented to the utmost and sharp classifying capacity can be obtained.