To fit a hanger door to the required position of a floor easily and surely by providing screw through holes on a fitting seat, and standingly providing a guide pin fitted into the fitting groove on the lower part of the hanger door.

A fitting seat 81 is provided with screw through holes 82, 83a, 83b on the positions corresponding to the respective apexes of an isosceles triangle. Next a guide pin 84 fitted into the fitting groove of the lower end part of a hanger door 5 is standingly provided between the two apexes, so as to form a door end side bracing tool 80. Next sash pulleys 70 mounted on a hanger rail 20 are combined with the hanger door 5, and moved up to the specified closed position. Succeedingly, the bracing tool 80 is fixedly secured to a floor face exposing the through holes outside the door end. Then the bracing tool 80 prevents side runout at the door end side during closing and at the intermediate part during movement. Because the guide pin 84 in previously inserted into the groove of the hanger door 5, the hanger door 5 is hung down on the closed position and the bracing tool 80 is fixedly secured in the condition being correctly positioned. Hereby, on the closed position on which the hanger door 5 is hung from the hanger rail 20, it can be firmly fixed to the floor face and can be detached.