To provide an agitator mill capable of treating a large amount of a grinding stock.

The agitator mill 1 is provided with a separate grinding material-auxiliary grinding body-separator device 24. The separator device 24 comprises a rotor 31, which is drivable to rotate, for separating the auxiliary grinding bodies 52 from the treated grinding stock. The auxiliary grinding bodies 52 are returned to the agitator mill 1 by untreated grinding stocks to be conveyed. The separator device 24 forms a closed system together with the agitator mill 1 and lines 22, 23 connecting the agitator mill with the separator device.