Seat slide device for a vehicle

A seat slide device (10) for a vehicle comprising a guide rail (2), which extends in the back/forth direction of the vehicle seat (95) and includes a fixed vertical side wall (24). The guide rail (2) is mountable on the vehicle floor (9), and a slide rail (3) is engaged with the guide rail (2) and guided to slide in the longitudinal direction of said guide rail (2). The slide rail (3) includes a vertical side wall (36) displaced from the vertical side wall of the guide rail (2) and attachable to the vehicle seat (95). The seat slide device (10) is characterized in that it further comprises a drive member (55) provided in a space (15) formed between the guide rail (2) and the slide rail (3) and rotatably supported by either one of said guide rail (2) or said slide rail (3) and a driven engaging portion (26) of the other of said guide rail (2) or said slide rail (3) which is engaged with said drive member (55).