To provide a workbench horizontally holding mechanism of a maintenance vehicle which is simple structure, can always hold a workbench horizontal in any curved section and can improve in workability and safety.

A lift guide pipe 2 is vertically provided two by two with a suitable space apart before and behind from both the right part of and the left part of upper surface of an under carriage 1 of a maintenance vehicle, a workbench 3 is supported to an upper end part of these lift guide pipes 2. Each lift guide pipe 2 is lifted by extending/contracting a lifting hydraulic cylinder 4 respectively adjacent thereto. An upper end part of front and rear two inner pipes 2b in a left side, of each lift guide pipe 2, is supported turnably singly by a pin 6 relating to a support frame 5 of the workbench 3, in the other hand, an upper end part of front and rear two inner pipes 2b in a right side is supported turnably by a roller 7 and a holding hydraulic cylinder 8 and movably in a lateral direction to the support frame 5.