The present invention relates to a bicycle. The bicycle according to the present invention comprises: a front wheel steering unit which comprises a front wheel, a fork, and a handle connected to the top end of the fork; a connecting frame which is coupled to the fork and is extended backwards; a main frame in which the front end is coupled to the connecting frame and the rear end is branched into two portions to be coupled to a rear wheel spindle; and a saddle part which is coupled to the top of the main frame; a rear wheel which is coupled to the rear wheel spindle to be rotated; a pair of driven gears, a pair of drive members which are in gear with the gear teeth of the driven gears; a pair of rack teeth; a pinion which is in gear with the rack teeth to be installed between the rack teeth; and a rear wheel rotating tool which is coupled to the driven gears and the rear wheel and transfers the driving force from the driven gears to the rear wheel only when the rack teeth rise.