To provide a bicycle which can be reduced in weight and be compactified without generating problems peculiar to a conventional bicycle having a gear/chain drive system.

In the bicycle the rear wheel hub 7 of which is rotatably provided to a bicycle body frame 1 and the rear wheel 3 is pivoted by the rear wheel supporting shaft 7, the drive mechanism 6 of the rear wheel comprises a pair of right and left drive shafts 8 pivoted by the bicycle body frame 1, a pedal mechanism section 9 supported by each drive shaft 8, a transmission wheel 10a fixed to each drive shaft 8, a transmission wheel 10b each fixed to both the ends of the rear wheel hub 7, a transmission belt 11 wound between the transmission wheels 10a and 10b respectively, and a transmission mechanism section 12 having a plurality of gears for transmitting the rotation of the rear wheel hub 7 to the rear wheel 3.