A bicycle for water and land comprising: a first floating means provided on and rotating together with a front wheel frame rotating in conjunction with handlebars, in such a manner as to be developed to both sides thereof by means of buoyancy generated when entering water to float the front wheel frame; a second floating means provided on a rear wheel frame in such a manner as to be developed to both sides thereof by means of buoyancy generated when entering water to float the rear wheel frame; and a plurality of propellers provided on a plurality of spokes disposed on the rear wheel frame in such a manner as to rotate together with the rear wheel frame to generate a propelling force therefrom, wherein the first floating means comprises: a first base frame fixed to the front wheel frames; a pair of first wings rotatable to both sides of the first base frame in such a manner as to be developed upward by means of buoyancy and to be rotated downward and folded if the buoyancy disappears; first stoppers adapted to restrict the developing angles of the pair of first wings; rudders rotatable on the inner surfaces of the pair of wings in such a manner as to have lower end portions oriented downward, while being folded to the inner surfaces of the pair of first wings if the pair of first wings is folded and being increased in the separated angles from the inner surfaces of the pair of first wings if the pair of first wings is developed, thereby conducting the steering in the advancing direction of the bicycle; and a first fixing means adapted to fix the pair of first wings folded downward to the front wheel framed, and wherein the first floating means and the second floating means are provided on the upper end portions of the front wheel framed and the rear wheel frame and are automatically developed upward from the upper end portions of the front wheel frame and the rear wheel frame by means of buoyancy if the bicycler is located in water, so that they are located over the rotary shafts of the wheels of the front wheel framel and the rear wheel framed, while being automatically folded by means of their self weight if the bicycle is escaped from water, and the rudders of the first floating means are substantially heavy in weight on the lower end portions thereof in such a manner as to be automatically moved downward upon the development of the pair of first wings. a first floating means provided on and rotating together with a front wheel frame rotating in conjunction with handlebars, in such a manner as to be developed to both sides thereof by means of buoyancy generated when entering water to float the front wheel frame; a second floating means provided on a rear wheel frame in such a manner as to be developed to both sides thereof by means of buoyancy generated when entering water to float the rear wheel frame; and a plurality of propellers provided on a plurality of spokes disposed on the rear wheel frame in such a manner as to rotate together with the rear wheel frame to generate a propelling force therefrom, a first base frame fixed to the front wheel frames; a pair of first wings rotatable to both sides of the first base frame in such a manner as to be developed upward by means of buoyancy and to be rotated downward and folded if the buoyancy disappears; first stoppers adapted to restrict the developing angles of the pair of first wings; rudders rotatable on the inner surfaces of the pair of wings in such a manner as to have lower end portions oriented downward, while being folded to the inner surfaces of the pair of first wings if the pair of first wings is folded and being increased in the separated angles from the inner surfaces of the pair of first wings if the pair of first wings is developed, thereby conducting the steering in the advancing direction of the bicycle; and a first fixing means adapted to fix the pair of first wings folded downward to the front wheel framed, and