Wheel shaft structure of monocycle

A wheel shaft structure of a monocycle, comprising a wheel rim, and a shaft assembly mounted in a center of the wheel rim, wherein:

• the shaft assembly includes a wheel shaft passed through the wheel rim and having two ends each combined with a crank set of the monocycle, so that the wheel shaft is driven and rotated by the crank set of the monocycle, two opposite single-direction bearings symmetrically mounted on the wheel shaft and received in a central hole of the wheel rim, and two opposite double-direction bearings symmetrically mounted on the wheel shaft and received in the central hole of the wheel rim.