A longitudinal adjuster for a vehicle seat (3) has a first seat rail (5) fixed to the vehicle structure and arranged on a vehicle floor (10) and a second seat rail (8) fixed to the seat and displaceable in relation to the first seat rail (5) and guided in same. A position detection device (20) is provided with a sensor (24), having a magnet and a Hall element. The sensor (24) is arranged in the interior of the second seat rail (8) and aligned with a flat area associated with the first seat rail (5) in which one end of the flat area corresponds to the end of the rail and the flat area forms a detection area. The sensor (24) is used to detect an end of the detection area. The sensor (24) has a certain detection range and the distance between the sensor (24) and the detection area lies within the certain detection range of the sensor (24). The distance between the sensor (24) and the vehicle floor (10) lies outside of the certain detection range of the sensor (24).