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, in this control method, the direction of motion of the mobile scaffold is only partially constrained by the wire. Thus, the device is greatly excited when an external force is applied. It is difficult to damp these oscillations in wire-reeling control. We designed a semi-active dynamic absorber for vibration control by applying the skyhook theory, a basic theory of the active suspension. When a random input that simulates the wind force was given to the mobile scaffolding device with the dynamic absorber, the vibration of the device was reduced by half compared with that of the mobile scaffolding device without the dynamic absorber.