A power slide device for a vehicle seat includes a lower rail and an upper rail slidable relative to the lower rail, a front support member fixed to the lower rail, a screw rod, a rear support member provided with a rear orthogonal plate portion and a fixed plate portion, a movement limiter which limits movement of the screw rod, a worm wheel, and a collision load receiving portion which limits forward tilting of the rear orthogonal plate portion by contacting the base surface of the lower rail when a force is exerted on the screw rod forwardly from the worm wheel. The collision load receiving portion is positioned in front of the rear orthogonal plate portion and is spaced downward from the screw rod and integrated with the rear support member that is mounted to the screw rod.