Abstract: A drive body (4) which is rotationally driven via a shaft (6) projects into a fixed housing (1) closed by a cover (2). The annular-gap-shaped grinding chamber (M) formed between the housing (1) and the drive body (4) is partially filled with grinding balls, for example to 75%, and grinding stock flows continuously through it. The grinding stock enters from a product inlet (8) via the inlet gap (7) into the grinding chamber and leaves the latter through the discharge gap (3) which does not let through the grinding balls.The grinding chamber (M) is continuously widened from the mouth of the inlet gap (7) up to a deflection point (U).This results in a better starting behavior and a substantially more effective grinding, because a considerably higher grinding ball filling ratio can be achieved at the same circulating time of the grinding balls.