| 摘要 |
PROBLEM TO BE SOLVED: To reduce the working burden of a worker. SOLUTION: When a stopper 12 (drooping bar 25) is descended, a rear portion of a lock member 23 receives a force pushing down it. Since the lock member 23 counter-clockwise rotates in Fig. 5, an upper edge portion of a through hole 24 at a side apart from a pivot shaft 22 is removed from the drooping bar 25 and a lower edge portion of the through hole 24 at a side near the pivot shaft 22 is also removed from the drooping bar 25. As a result, a descending of the stopper 12 is permitted.
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