To provide a monocycle with a buoyancy bag which is reduced in physical load to gravity, large in drag to fall-down, and contributes to exercise every part of the body.

The monocycle 10 is moved by pedaling by a leg force in water same as on the ground. The buoyancy bag is attached to an upper saddle 12 or molded, or the buoyancy bags of various shapes are installed at the lower part of a saddle periphery or in the fore-and-aft direction, the action of buoyancy is adopted on the saddle and the peripheral part, and the monocycle stands by itself in a state of rest in water.