To enable free travelling on a newly snowed road, pressed snow road, frozen road, or the like by providing a sliding body and a mechanism to vertically move the same on a front side suspension system, providing an auxiliary wheel supported through an auxiliary member on a rear side suspension system and providing a belt used for a winter period road to be trained over a rear wheel and the auxiliary wheel.

When a bicycle 2 is allowed to travel on a newly snowed road, pressed snow road, frozen road, or the like, a vertically movable mechanism 18 is operated to lower a sliding body 16. The vertically movable mechanism 18 is locked so that the bottom surface of the sliding body 16 is located by the height H above the installing surface of a front wheel 8, while an auxiliary member 84 is swung so that an auxiliary wheel nearly makes contact with a road surface. Thus, the front wheel contacts the road surface on the front side and the front wheel 8 is supported by the sliding body 16. Also, a belt 94 for winter period road contacts the road surface on the rear side between a rear wheel 12 and auxiliary wheel 90 to enable free travelling of the bicycle 2 on the newly snowed road, pressed snow road, frozen road, or the like.