A vehicle seat longitudinal adjustment device has a floor rail, a seat rail, and a locking unit substantially accommodated in a cavity formed by the rails, and a housing. A bearing shaft is disposed in this housing and extends in the displacement direction. The device includes at least two flat blocking parts, pivotable independently of each other about the bearing shaft and elastically biased, independently of each other, by one blocking spring each, and a releasing part. The structurally identical blocking parts each have two arms, between which the bearing shaft is located. The seat rail has, for each blocking part, shear slots accommodating the first and second arms. The floor rail has a perforated strip cooperating with the first arms, with first blocking slots, and a perforated strip cooperating with the second arms, with second blocking slots. The slots are periodically disposed one behind the other in the displacement direction.