The present invention relates to a device for the automatic adjustment of the pretension of a pulling element (10, 11) in particular a cable, comprising an elasticity element (50) acting on a first mounting means (20) for a first section (10) of the pulling element for increasing the pre-tension, a second mounting means (30) for a second section (11) of the pulling element, threads (70, 70′, 71) arranged at the first mounting means which interact with a spindle (40, 40′) so that a change of the distance between the first mounting means (20) and the second mounting means (30) causes a rotation of the spindle (40) or the threads (70), and blocking elements (36, 45; 236, 245), which are arranged such that they block a rotation of the spindle or the threads (70), respectively, when the pulling element is under pulling load.