The invention discloses an
electric power assisting device for bicycles, which is characterized in that the device comprises a middle axle, a gearless
flywheel and a chain wheel, wherein the middle axle is arranged on a bicycle frame, the gearless
flywheel is assembled on the middle axle by a gearless
flywheel overrunning
clutch, the chain wheel is fixed on the gearless flywheel, and the chain wheel is connected with a flywheel fixed on a rear bicycle wheel by a chain; the
electric power assisting device for bicycles also comprises an electric driver and an electrically driven
sprocket; the electric driver comprises a shell, a motor, a
planet gear reducing mechanism, an inner gear ring, an inner gear ring overrunning
clutch and an output shaft, wherein the shell is fixed on the bicycle frame, and the motor, the
planet gear reducing mechanism, the inner gear ring, the inner gear ring overrunning
clutch and the output shaft are arranged in the shell; a rotating shaft of the motor is in transmission connection with the inner gear ring by the
planet gear reducing mechanism; the inner gear ring is assembled on the output shaft by the inner gear ring overrunning clutch; the output shaft extends out of the shell and is fixed with the electrically driven
sprocket; and the electrically driven
sprocket is meshed with the chain. The
electric power assisting device for bicycles, disclosed by the invention, is simplified in structure, stable in operation and large in output torque, and can greatly enhance the climbing capacity of an
electric bicycle.