The seat has a backrest (1), which may be locked in various normal positions, and may be folded forward. The folding movement is transmitted via a lever to a lock (2). This locks a lower rail (3) into a locking position (4) on the vehicle body when the backrest is in normal position. When the backrest is folded forward, the lock is released by the lever. The lower rail, as well as an upper rail (11) with the seat fastened to it, are moved forward in the vehicle in the relative position they occupied before the lock was released.