| 摘要 |
PROBLEM TO BE SOLVED: To suppress lateral bending without obstructing the view.SOLUTION: An inner mast 3 includes: a pair of left and right mast materials 30L, 30R extending in an upward and downward direction; beam materials 31a-31d for connecting the pair of mast materials 30L, 30R; and a center guide rail 32 extending in the upward and downward direction between the pair of mast materials 30L, 30R. The center guide rail 32 is composed of: a front rail material 33 disposed on a front side of the beam materials 31a-31d; and a rear rail material 34 disposed on a rear side of the beam materials 31a-31d. The inner mast 3 further includes a reinforcement plate 38 disposed between the front rail material 33 and the rear rail material 34, for joining a rear face of the front rail material 33 and a front face of the rear rail material 34. Left and right side faces 38L, 38R of the reinforcement plate 38 extend along left and right side faces 33L, 33R, 34L, 34R of the front rail material 33 and the rear rail material 34. |
