PURPOSE: To provide an output shaft structure whereby a transmission can be made compact and lightweight by reducing the number of components while preventing quench cracking of an output shaft and lowering of the shaft strength.

CONSTITUTION: An output shaft 105 passing through an internal fixed shaft 103 extends protrusively from the rear end face 101 of a transmission housing 100 and has an integrally molded flange 110 at its projecting end. A rearwardly extending portion 104 is formed in the internal fixed shaft and a bearing 118 is held thereto. The bearing supports the end portion of the output shaft with the outer peripheral surface of the output shaft 105 as an inner race. The number of components for connecting a propeller shaft is thereby reduced, and because only the output shaft extends outside of the transmission housing, the bearing size and the outer form of the end portion or the transmission housing are both reduced so that the output shaft structure can be made compact. The output shaft has no suddenly changing part in its cross section, thus avoiding quench cracking and lowering of its strength during heat treatment.