Speed gear are manufactured by integrally molding, by either hot or warm forging, a speed gear section and a clutch spline section. Teeth of the speed gear in the speed gear section and an involute spline parallel to an axial line of the gear in the clutch spline section are rough formed. The involute spline parallel to the axial line of gear formed on the section of clutch spline is formed, by cold forging, into an involute spline with a back taper having a chamfer at the tip. The teeth of the speed gear formed at the speed gear section are finish formed by forming the speed gear teeth by rolling dies, by cold forging, while turning them around a shaft hole with reference to the clutch spline section forming the involute spline with back taper. A speed gear having a speed gear section and a clutch spline section including speed gear teeth and an involute spline with a back taper having a chamfer at the tip is thereby provided.