| 摘要 |
PROBLEM TO BE SOLVED: To provide a boom standing-up and falling-down device of superior stability in the standing-up and falling-down operation for the boom. SOLUTION: A pair of booms 13, 13, left and right, positioned on both of left and right sides of an up and down guide pillar-shaped member 18 are changed in their postures to the spreading state to the left and right sides by a boom up and down standing-up and falling-down mechanism 20 while moving upward, respectively, and also their postures are changed to the upward closed standing-up state while simultaneously moving downward. A pair of booms 13, 13 are held in the state of the relation of positioning symmetrically, left and right, at all times through the up and down guide pillar-shaped member 18 all through not only when they are standstill but also all through the processes of being operated by the boom up and down standing-up and falling- down mechanism 20. The balance between the left and right when the booms are stood up and fallen down, therefore, can be securely retained.
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