To realize a single fixation system on a floor surface, improve the operability for releasing fixation, prevent a fixation mechanism from being exposed, and provide satisfactory appearance.

A flush bolt 5 for fixing a floor surface is built in a lower end part, the flush bolt 5 is provided with a rack 6 and a pinion 7 which mesh mutually, and the rack 6 rises, lowers, and moves vertically in accordance with the rotation of the pinion 7 so that it can come in and out from a lower end of a movable partitioning wall. A rotary shaft 8 of the pinion 7 is stretched horizontally on the movable partitioning wall, its end face is arranged on a wall face formation face of the movable partitioning wall, and the blush bolt 5 can be operated on the wall face formation face of the movable partitioning wall.