To improve a fall in grinding efficiency caused by returning aggregates not required for being ground by a vertical grinder to the vertical grinder for grinding when grinding cement clinker using a two-stage type grinding facility of the vertical grinder and a ball mill.

A classification apparatus of this invention can only change the rotary frequency of a dispersing plate without changing the rotary frequency of a classifying vane by separately providing driving machines for the classifying vane and the dispersing plate for grinding the aggregates, so that the aggregates are hardly ground without changing the degree of classification, thereby improving the fall in the grinding efficiency by the aggregates. Additionally, when the particle size of raw materials taken out of the classification apparatus as fine particles is set at DP80≤150 μm, the grinding efficiency of the ball mill is improved. Moreover, when a storage facility for raw materials is provided between the classification apparatus and the ball mill, the raw materials ground by the vertical grinder are stored in the storage facility, and the ball mill is operated only at night with low energy charge, thereby achieving an efficiency in the apparatus.