Abstract: A vehicle seat belt tightening system for taking up slack from a seat belt in high acceleration or deceleration condition to positively restrain a vehicle occupant but otherwise permitting the seat belt to be paid out to accommodate a movement of the vehicle occupant, comprising: a retractor unit comprising a winding spool, a seat belt tightening unit arranged at a seat belt outlet end of the retractor unit, a drive unit for selectively activating the seat belt tightening unit, and a deceleration detection unit for acting upon the seat belt tightening unit, which are integrally mounted on a common frame. Thus, the reliability of the system is improved and the installing and the servicing of the system is simplified.