| 摘要 |
Bosses extending in the boom width direction are provided in a front end part of a main boom body rotated upward, and hooks opening downward are provided in a base end part of an extension boom body rotated downward. The above hooks and the bosses are arranged so as to satisfy a condition that at the time of second relative rotation by a two-step pin hole matching method of matching pin holes in order from the upper side and with a different center, the hooks and the bosses are moved away from each other while lower pin holes are matched with each other. |
