An invention relating to a tensioning device for the belt or chain drive of a stirred ball mill and to a stirred ball mill. The tensioning device includes a tensioning lever which is arranged on a rotatable tensioning foot and which includes a tensioning wheel. A rotatable adjusting disk with a guide contour is arranged on the rotatable tensioning foot. The position of the adjusting disk can be fixed on the machine housing of the stirred ball mill by means of a securing means paired with the guide contour of the adjusting disk. The tensioning device further includes a longitudinally variable tensioning element for rotating the adjusting disk relative to the machine housing of the stirred ball mill.