PURPOSE: To achieve dry classification of wet raw material containing a large amount of powder by a method wherein a classifier is installed at the lower part of a sucking and exhausting hole and the gap between the bottom rotating pan and a neighbor rotating pan is changed freely.

CONSTITUTION: When a rotating separator 12 as a classifier, a reduction gear motor 2 and a screw conveyor 15 are dried and wet raw material is thrown into a rotating pan 6 from a supply hole 11, the raw material falls down by the pan 6 and exchanges heat with hot gas and comes in contact with upward hot gas from a blade ring 10 and then is blown up upwards. Particles with large diameters fall down on the dish 6 again and hereafter the same circulation is repeated. Fine particles are carried to the separator 12 and pass through the rotating blades 12d of the separator 12 and are discharged from a sucking and exhausting hole 13 outside the drier. In order to discharge middle size particles and coarse particles the bottom rotating pan 6e is lowered to expand the gap 6Y. Total amount of hot gas supplied from a supply hole 14 is not changed, but as the amount of hot gas flowing into the gap 6Y is increased, the amount of hot gas flowing into the ring 10 is reduced to reduce a gas velocity and the coarse particles fall down and move toward the the conveyor 15.