A speed change device for a bicycle comprises a carrier jointed to a crank arm and a plurality of planet gears rotatably supported on a plurality of shafts arranged in a circle on said carrier. Each of the planet gears includes a plurality of planet gear elements different in number of teeth. The device further comprises an internal gear in mesh with ones of the planet gear elements of the planet gears and formed in an outer circumference with a sprocket to form a driven rotary body, one-way clutches for connecting the driven rotary body to the carrier, a plurality of sun gears provided on a crankshaft and in mesh with the planet gear elements of the planet gears, respectively, and one-way clutches provided between inner circumferences of the sun gears and a fixed bearing enclosing the crankshaft. One of the one-way clutches last mentioned is able to connect selectively.