| 摘要 |
<p>The danger of the jib falling due to various operational errors is eliminated during both the operation of extending the jib from the stowed position thereof and the operation of stowing the jib from the extended position thereof. A jib (2) is variously provided with a fulcrum pin engagement status detection means (5), a fulcrum pin disengagement restriction means (7), a connector pin engagement status detection means (6), a connector pin disengagement restriction means (8), a first correlation means (91), and a second correlation means (94), wherein movement of a connector pin (40) toward the disengagement side is restricted by the connector pin disengagement restriction means (8) via the first correlation means (91) when the fulcrum pin engagement status detection means (5) detects that a fulcrum pin (30) has been disengaged, and movement of the fulcrum pin (30) toward the disengagement side is restricted by the fulcrum pin disengagement restriction means (7) via the second correlation means when the connector pin engagement status detection means (6) detects that the connector pin (40) has been disengaged, whereby both the fulcrum pin (30) and the connector pin (40) cannot be (simultaneously) disengaged during either the jib extension operation or jib stowing operation even when operational errors occur.</p> |
