Rail device for vehicle seat

An embodiment rail device includes an upper rail, a first bearing support on the upper rail, a lower rail, a bearing connection end on the lower rail and inserted into the first bearing support, a vertically elongated bearing contact adjustment hole on the lower rail, an upper bearing rotatably connected to the bearing connection end and in close contact with a floor of the first bearing support, a lower plate including a fastening groove that receives a lower end of the lower rail, a bearing shaft mounting hole on a wall surface portion of the fastening groove and matched with the bearing contact adjustment hole, a second bearing support outside the fastening groove and having an opened upper portion, a lower bearing rotatably disposed within the second bearing support, and a bearing shaft fastened to the bearing shaft mounting hole and the bearing contact adjustment hole by a screw.