The present invention relates to an adjustment device for adjusting the inclination of the backrest (14) of a seat (10) of a vehicle, which allows to perform both quick adjustments of large angular amplitude and fine adjustments. According to a possible embodiment of the invention, the adjustment device comprises separate control elements (20, 22) for performing quick adjustments and fine adjustments, respectively, of the inclination of the backrest (14). According to another possible embodiment of the invention, the adjustment device comprises a single control element (20) for performing both quick adjustments and fine adjustments of the inclination of the backrest (14).