| 摘要 |
PROBLEM TO BE SOLVED: To set a cylinder speed at the same level both in derricking action and in telescoping action for letting falling and telescopic action of a jib coincide with rising and contracting action in a falling direction of an operation lever. SOLUTION: This device is provided with a derricking cylinder to let a jib derrick from the underside, an expansion cylinder 19 to telescoping the jig, a change-over switch 23, a derricking switching valve gear 25 switched by the change-over switch 23, and a hydraulic pressure direction switching valve 29 to supply hydraulic oil to either of both cylinders through the switching valve gear 25 to be capable of switching between a first and a second switching positions in accordance with a tilting direction of the operation lever. The first switching position hydraulic oil side is connected to the bottom side of both cylinders, and the second switching position hydraulic oil side is connected to the head side of both cylinders. A reversing means 30 interlocked with operation of the change-over switch 23 to reverse a switching action direction of the hydraulic pressure direction switching valve 29 is provided.
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