To realize a steering device having a high degree of freedom of design with a simple structure by eliminating an inevitably caused bump steer, and a vehicle convertible without disassembling by simple operation of using its steering device, in the vehicle for operating a steered wheel by a link mechanism.

Since an increase-decrease in an angle difference in the twist direction between a knuckle arm and a steer arm caused by the vertical movement of a wheel, is absorbed by rotating the steer arm in the twist direction by installing the steer arm on an outer ring of a constant velocity joint by using a 4-node link mechanism for the steering device, the bump steer is eliminated without having influence on an angle in the steering direction. One end of a suspension unit for suspending a longitudinal swing arm is connected to a rockably pivoted seat post, so that the longitudinal swing arm can also be simultaneously folded up by interlocking with folding-up of the seat post.