PURPOSE: To eliminate self-dusting characteristics from polishing cloth, and also, to facilitate a replacement by pushing and feeding a pachinko ball by a blade of a screw tube rotated in a polishing cylinder, rubbing it against the polishing cloth which is installed along an inner wall of the polishing cylinder and is excellent in water absorbency and oil absorbency and grinding it.

CONSTITUTION: In a grinding cylinder 1, polishing cloth 5 is inserted along its inner wall, and also, a screw tube 6 having a blade 10 of a suitable pitch for rotating in the direction as indicated with an arrow A around an axis of the polishing cylinder 1 is installed. Between the inside surface of the polishing cloth 5 and the surface of the screw tube 6, a clearance being roughly equal to or a little smaller than the diameter of a pachinko ball 2 is provided, and the pinball 2 thrown into the polishing cylinder 1 from a throw-in port 3 is rubbed against the polishing cloth, while being pushed and fed by the blade 10 and polishing is executed.