A bicycle according to the present invention comprises of a steering axis and an axle of rear wheel that are attached in one unit with a frame to build a form; a pair of guide members with guide holes formed therein are attached to both cut ends of the frame; a pedal axle with the attachment of pedals and a rotating gear in a unit are respectively assembled and fixed onto the guide members; the bicycle according to the present invention comprises a crankshaft of which a pair of crank cams is assembled and fixed into both cut ends of the frame; a gear which engages with the gear; and a spindle which supports a unit of the gear and a sprocket to rotate; the bicycle according to the present invention is run by a running system in which the crank cam rotates when the pedals are reciprocated up and down.