A seat slide device with a walk-in mechanism comprises a stationary guide rail fixed onto a floor panel and a slidable guide rail slidably fitted to the stationary guide rail for fore-aft position adjustment of a seat, a screw-threaded shaft member rotatably supported on one of the slidable guide rail and the stationary guide rail, and a nut member engaged with the screw-threaded shaft member for causing fore-aft motion of the slidable guide rail to the stationary guide rail through rotation of the screw-threaded shaft member. The walk-in mechanism includes a lock member being operable between a locked position to interlock the nut member to the other guide rail, and an unlocked position to permit a change of relative position of the nut member to the other guide rail. The lock plate is pivotally shifted between the locked position an the unlocked position by a control cable usually linked to a reclining lever.