| 摘要 |
PROBLEM TO BE SOLVED: To provide a boom apparatus which can freely open or close a side boom in the horizontally and vertically rotating directions, does not require height at the time of housing, and is tough enough to stand contact with obstacles and economical. SOLUTION: At the time of moving a side boom 17 from the housing position to a horizontal position relatively to a center boom 1, at first the side boom 17 is turned in the horizontal direction and then turned in the vertical direction to position the side boom 17 and the center boom 1 on the same straight line. A boom extension bracket 8 is hung by a spring 13, so that the horizontal movement and the vertical movement are made possible using only a single motor-operated cylinder 3 with a small capacity.
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