Abstract: A tensioning mechanism for a safety belt reel-in mechanism, including a cable drive that is activatable in the event of a crash and includes a cable pulley that is adapted to be positively coupled with the belt reeling-in shaft of the reel-in mechanism via a locking member that is disposed on the cable pulley and is radially shiftable for meshing with coupling teeth provided on a toothed ring of the belt reeling-in shaft. To assure a more reliable tooth engagement in every phase of the tensioning movement, the cable pulley is provided with a support arrangement that is adapted to rest against the tooth ring of the belt reel-in mechanism and that extends into a plane formed by the locking member and the coupling teeth.