PURPOSE: To finely pulverizing a stock material to form a stock powder without contaminating the same, by arranging a impact disc integrally rotating along a stirring blade, a motor for rotating a rotary shaft so as to freely vary the rotary speed thereof and a vacuum pump for exhausting steam in a bowl.

CONSTITUTION: After an ultra-fine stock material with a sub-micron particle size for ceramics is charged in a bowl 1 from a charging port 16, a predetermined amount of pure water is injected in the bowl 1 and a stirring blade 5 is rotated to prepare a slurry. A heating medium is passed through a jacket 2 to heat a bowl 1 and, after dehydration and driving are advanced, the number of rotations of the stirring blade 5 are-increased to perform granulation operation. In this case, the stirring blade 5 rearwardly inclined at an angle θ allows a high viscosity cake not only to spring up at a high speed but also to be impinged to an impact disc 6 rotated at a high speed at the upper part and, therefore, the drying of the lumpy cake is promoted and the cake is gradually divided and granulated to obtain particles with a definite particle size.