We are currently developing a mobile scaffolding device that can dodge the piers of bridges without dismantling the scaffold when moving between spans to improve efficiency and safety in bridge inspections. The mobile scaffolding device treated in this paper is split in the center of the device when it crosses the piers. In this process, the mobile scaffold is cantilevered and poses a danger to the workers on board. Therefore, we implemented horizontal holding control by wire reeling to keep the mobile scaffold horizontal. However, mechanical analysis and investigation of the mobile scaffold device have been insufficient in the previous studies. Especially, the wire constraint position corresponds to the arm length of the moment generated by the wire tension. Therefore, it is inferred that the wire constraint position has effects on the horizontal holding performance. Therefore, in this paper, several candidates for the wire constraint position were obtained, and the horizontal holding performance was compared and verified at each position. As a result, it was found that by setting the x-coordinate of the wire constraint position close to the wire reeling mechanism and the ycoordinate at the bottom of the scaffolding, highly stable horizontal holding control can be achieved with small wire tension.