To improve workability by a method wherein a support shaft body, to which an approximately square-shaped head section, in which a corner section is rounded, is formed, is inserted into a socket, to which an approximately square-shaped through- hole, in which a corner is rounded, is formed, the inclined plane section of a bracket metal is formed in broad width and notched in a V shape in a plan view, and a stopper clamping the bracket metal to a rail is introduced from the strip groove port of the rail.

This support shaft body 1 is constituted by assembling a socket 2, a support shaft body 3, a cover body 4 and a spring 5. The head section 3c of the support shaft body 3 energized by the spring 5 is abutted against the internal surface 2d of the internal flange 2a" of the socket 2 in the support shaft body 1, the greater part of the shaft section 3b of the support shaft body 3 is projected from the front end of the socket 2, and the support shaft is held to the socket 2 under the freely forwarding-retreating state, in which the front end section 3b is retreated when it is pushed at constant pressure in the socket 2 direction and repulsed when it is separated. A section lower than a flange section 2a is pressed into a top face at the side end of a door and the door is mounted in the support shaft body 1.