| 摘要 |
PROBLEM TO BE SOLVED: To reduce the depth of a truss by overlapping a rear wheel of a step travelling in a forwarding passage and a rear wheel of a step travelling in a backwarding passage with each other in a vertical direction. SOLUTION: A rear wheel 17 of a step 11 is provided to be movable with respect to a front wheel 16 in the cross direction of a step 11 and a rear wheel rail 22a on the forwarding passage side and a rear wheel rail 22b on the backwarding passage side are provided to approach each other in the vertical direction and shift each other in the cross direction of a truss 1. The end of the rear wheel rail 22a on the forwarding passage side is connected to the end of the rear wheel rail 22b on the backwarding passage side via a reversing rail and the rear wheel 17 of the step 11 travelling in a forwarding passage is overlapped with the rear wheel 17 of the step 11 travelling in a backwarding passage in the vertical direction. When the rear wheel 17 of the step 11 travelling in the forwarding passage is transferred to the rear wheel rail 22b on the backwarding passage side via the reversing rail, the rear wheel 17 of the step 11 is moved with respect to the front wheel 16 in the cross direction of the step 11.
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