| 摘要 |
PROBLEM TO BE SOLVED: To provide a back stop device even when a large space cannot be secured between a main frame and a boom. SOLUTION: The back stop device 52 is compactly composed of a bracket 53 installed on a front support arm 24, a boom receiving member 57 movably installed on the bracket 53, and a spring 61 arranged between the bracket 53 and the boom receiving member 57. Thus, even when the large space cannot be secured between the main frame 5 and the boom 9 by arranging the front support arm 24 in the main frame 5, the back stop device 52 can be arranged in a narrow space between the front support arm 24 and the boom 9 so that the occurrence of excessiveness of a derricking angle of the boom 9 can be surely regulated by this back stop device 52.
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