A seat lifter for height adjustment of vehicle seat, which has a lifter linkage for vertical movement of the seat and a drive mechanism therefor. The lifter linkage includes a pair of links, a bell
crank portion formed in one of the two links, and a rotation transmission link element including a sector gear which is operatively connected with the bell
crank portion. The drive mechanism comprises a
ratchet-type lever mechanism operatively connected via a
brake unit with the lifter linkage, the arrangement of which
ratchet-type lever mechanism is such that only one-
stroke operation of a lever causes a
ratchet pawl member to rotate so as to bring a selected one of its two toothed ratchet pawls to meshed engagement with a
mating one of two ratchet gear wheels, thereby allowing for automatically selecting a desired operative direction without any switch-over operation and then continuously transmitting a certain amount of rotation force to the lifter linkage, so that the vehicle seat can easily be raised or lowered to a certain level.