| 摘要 |
There is provided a boom assembly bent at the center in a longitudinal direction so as to form a round shape protruding upward when seen from the side, comprising; a front boom sub assembly (47), the front boom sub assembly constituting the front of the center in the longitudinal direction of said boom assembly; and a rear boom sub assembly (48), the rear boom sub assembly constituting the rear of the center in the longitudinal direction of the boom assembly, wherein the front boom sub assembly (47) and the rear boom sub assembly (48) are symmetric when seen from the side, and portions from the midway positions in the longitudinal direction of the front boom sub assembly (47) and the rear boom sub assembly (48) to the center in the longitudinal direction of the boom assembly (12) have upper surfaces of arc shape protruding upward when seen from the side, and portions from the middles in the longitudinal direction of the front boom sub assembly (47) and the rear boom sub assembly (48) to ends in the longitudinal direction of the boom assembly (12) have upper surfaces of linear shape when seen from the side. |
