Disclosed is a seat sliding apparatus for a vehicle, the apparatus provided with a pair of lower rails fixed to the vehicle floor and a pair of upper rails fixed to a vehicle seat. The seat sliding apparatus causes screw shafts supported at the upper rail to rotate relative to nut members fixed to the lower rails and the upper rails to move relative to the lower rails in the seat forward-rearward direction. A speed reducer-equipped motor comprises a motor, a gear mechanism, and a gear housing. The gear housing is designed so that the axis of the output shaft of the gear mechanism extends in the seat width direction. A manipulation switch comprises a manipulating portion fixed to the gear housing such that the operation switch is exposed at a forward end of the seat.