Bicycle

A bicycle comprising:

• a frame on which a front wheel and a rear wheel are mounted to allow a user to ride while lying with a face of the user down;
• and
• an acceleration device mounted on the rear wheel to generate a power and perform acceleration according to pedaling;
• wherein the acceleration device includes:
• a main bracket mounted on ends of rear and bottom tubes;
• a pedal shaft provided on the main bracket with a one-way bearing interposed between to transmit a power in a forward direction and perform idling in a rearward direction;
• pedals coupled to both sides of the pedal shaft, respectively;
• a driver gear provided on one side of the pedal shaft to generate the power through a rotation of the pedal shaft;
• a switching shaft provided on an auxiliary bracket, which is maintained between main brackets by a supporter, with a bearing interposed therebetween;
• a mediating gear provided on one side of the switching shaft so as to be engaged with the driver gear;
• an acceleration gear mounted on a lateral side of the mediating gear;
• a driving gear provided on the pedal shaft, which is provided on a lateral side of the driver gear, with a bearing interposed therebetween so as to be engaged with the acceleration gear to output an accelerated power;
• and
• a hub fixed to the driving gear and mounted at the ends of the rear and bottom tubes to drive the rear wheel,
• wherein the driver gear, the switching shaft, the mediating gear, the acceleration gear and the driving gear are provided within the hub, and the pedal shaft passes through central portions of the hub, the main bracket and the rear wheel.