An exercise bike, comprising two footboards, six wheels, and four straight shafts with trapezoid-headed ends, is provided. Symmetrically arranged in the disk of each wheel are two eccentrical trapezoid apertures. The ends of the shafts are orthogonally inserted into the trapezoid apertures of the wheels, to form a wheel frame, thus avoiding the possibility of assembling the exercise bike improperly. The wheels are arranged in three lines, and the middle portions of the shafts are supported by bearings at the bottom of the boards and can rotate freely thereon. The bike can further be assembled into a safety-type exercise bike, or a massage-type one. When the footboards are threaded, the bike will move forward in a fluctuating manner. The various parts can leave the factory in separate packages for the customers to assemble on their own. The products can therefore be transported in large quantities and over long distances.