The Honshu-Shikoku Bridges (HSB) are comprised of 17 long-span bridges which span over the straits, and the bridge girders are at high altitude above the sea. Honshu-Shikoku Bridge Expressway Co., Ltd. is conducting maintenance management of the long-span bridges based on the concept of preventive maintenance, in which action is taken before deterioration progresses. Routine inspection of bridge girder at high altitude and repair painting requires securing safety and high work efficiency. For this reason, it is necessary to approach as close as possible to each member of the bridge girder. Against such a background, existing maintenance vehicles were modified and expanded the accessible range. In this paper, the technical development of the maintenance vehicle of the Ohnaruto Bridge by expanding the accessible range to the bridge girder is described.