An adjusting device for a deflection fitting of a vehicle safety belt system includes a rail provided with catch openings, and a slider mounted displaceably in the rail. The slider is adapted for connection to the deflection fitting and is provided with a detent mechanism for cooperation with the catch openings. The slider is further provided with a locking element which is functionally independent of the detent mechanism. The locking element is mounted at the slider pivotally between a neutral position in which it does not engage the rail, and a locking position in which it engages the rail and locks the slider in place.