Seat slide device for vehicle

The invention provides a seat slide device for a vehicle. The seat slide device for the vehicle is provided with a lower rail, an upper rail, and a lock mechanism which is capable of restricting the relative movement of the upper rail. The upper rail has a pair of side wall sections facing each other in the widthwise direction. The lock mechanism is provided with a lock lever having a pivot axis intersecting both the side wall sections and supported by the upper rail so as to be capable of swinging. Either the lock lever or the upper rail is provided with a deformation prevention member disposed between both the side wall sections, and this can prevent the deformation of the upper rail, which reduces the gap between both the side wall sections.