A centrifugal air classifier, in which a relation between an area S1 of a side surface of a cylinder or a truncated cone circumscribed about the rotor blades, an axis of the cylinder or a truncated cone being the rotor rotational shaft, and a calculation average value D of a diameter of a circle orthogonal to the rotor rotational shaft and circumscribed about the rotor blades is S1/D2=0.9 to 1.6, and with the S1, a relation between a cross sectional area S2 of inflow of the air for classification and the D is S2/D2=0.8 to 1.4.