| 摘要 |
A cast with an inherent function of automatically changing the direction of a wheel (11) is selectively stopped. A severe shock applied to the wheel (11) cancels the lock on the wheel (11) against the change of direction. In response to such shock, a wheel attaching member (12) is turned around the axis of a pivot shaft (13), whereby a key member (20) held by the wheel attaching member (12) escapes from a fitting recess (29a or 29b) formed in a fixed bushing (27). As a result, the rotary bracket (4) is allowed to rotate around the vertical shaft (5).
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