To effectively use a lock member for a wheel as a cover member when it is not used.

A pillion step holder 8 is provided to a sub pipe 7 connected to a seat rail 6, and the pillion step holder 8 is connected to the seal rail 6 by a stay 10 for a first lock member. Also, a stay 11 for a second lock member extending from the seat rail 6 is provided to a rear side of the stay 10 for the first lock member, and a holder 32 is mounted to the stay 10 for the first lock member and the stay 11 for the second lock member. The holder 32 is integrated with an elastic body 34. When a lock fitting 13 constituting a U-shaped lock device 12 is inserted in the holder 32 and the tip the fitting is locked toward a key cylinder part 14, the U-shaped device 12 is supported by a vehicle body side face on a side of a rear wheel and functions as the cover member.

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