A vertical mill composed of a rotor to stir up beads and a mill container to be filled with beads. The rotor is formed into a pin shape excellent in stirring, the mill container has a jacket structure for cooling, and the body equipped with a raw slurry feeding port on the container top and a variable-slit Cone- Separator to isolate beads from the product slurry on the bottom.

 In operation, raw slurry is supplied from the top of the mill and while descending inside the mill with a plug-flow like movement, beads are thrust downward by the fluid resistance build up, so that an effective atomization takes place due to the beads pressure coupled with the impact developed there. At the stage where raw slurry reaches mill lower part, beads and product slurry are separated by the function of variable-slit cone separator being displaced according to the inside pressure, and the beads retain inside the mill while the product slurry alone is recovered.