A speed change gear shaft for a bicycle having an internal speed change gear. The speed change gear is of the internal multistage type, and a speed change gear shaft is provided separately from a crankshaft of the bicycle. A swing arm on which a rear wheel is supported is supported for rocking motion on a main frame a rocking shaft. Since the speed change gear is disposed in the proximity of the rocking shaft, the fluttering of a chain can be suppressed small. Moreover, since the rocking shaft need not necessarily be disposed in the proximity of the crankshaft, the degree of freedom in design increases. Also, because the speed change gear shaft is disposed forward of the rocking shaft, the fluttering of the chain can be minimizer.