Abstract: The invention relates to a speed regulator of a bicycle, which speed regulator is in the rear hub or the pedal centre of the bicycle, which includes one or more hydraulic pumps which is rotated by a rear pinion or by the pedals, which hydraulic pump rotates one or more hydraulic motors, which hydraulic motor/hydraulic motors rotates/rotate the rear wheel of the bicycle. According to the invention, the rotation speed of the hydraulic pump can be steplessly changed when the rear pinion or the pedals rotate at constant speed.