A device is structured to be integrated with a major components such as a movable unit and a stator contained in a rail member for easy removal from downward of the lintel, thus eliminating adjustment work on site. Since the door may be simply installed on the hanger, it can be easily installed and removed. Also, the stator and the hanger with rollers may be connected by clamping a projection strip formed on a bottom face of the stator from left and right sides thereof with the hanger with rollers installed on the door, or instead by engaging the hanger with rollers with an engagement portion provided on the stator from both side thereof. Consequently, connecting and releasing of the stator and the hanger is simplified and the ease of maintenance is improved.