To solve the following problems: when a crank pedal is mounted integrally on the inner core shaft of a front wheel sprocket, strong power is needed for pedaling against a head wind or on an uphill.

A bottom bracket 1 is formed into a drum-shaped to be almost as large as a front wheel sprocket 2. A crank pedal 3 is attached closer to the outside of the front wheel sprocket 2. The drum 1 and the front wheel sprocket 2 are integrally attached. An opposite crank pedal is attached closer to the outside of the drum. A shell 4 is enlarged to conform to the drum to move a crankshaft outward. A sliding bearing is attached to the outer periphery of the drum 1 and the inside of the shell 4. Various sliding materials made of iron or plastic are used according to the purpose of use.