Abstract: A preliminary size reduction device for a ball mill or agitator ball mill and a ball mill with a preliminary size reduction device, wherein the preliminary size reduction device is disposed between a grinding stock inlet of the ball mill or agitator ball mill and a grinding chamber and includes a first size reduction mechanism constituted stationary and a second, rotationally mobile size reduction mechanism, between which a size reduction gap is formed. The first size reduction mechanism constituted stationary is a size reduction ring disposed in the grinding container.