Abstract: An automatic gear shifting device for multi-speed bicycles. According to the invention, the device comprises a centrifugal force gear shifting mechanism which is controlled by the pedaling cadence of the rider. Pedal crankshaft speed is transferred to a main unit which contains an axially mounted drive shaft. Flyweights which are pivotally affixed to the drive shaft by an inner sleeve engage the housing thread members once a rider pedals outside of a predetermined cadence range. Engagement of the threaded members causes the inner sleeve to move one position. A cam follower affixed to the inner sleeve thereafter causes rotation of an outer ring, the outer ring having upshift and downshift cable attached to it. Movement of the cable causes rotation of a cable drum which is pivotally mounted to a derailleur. Movement of the cable ring drum causes the derailleur to shift gears. Also provided is a means to adjust the cadence range.