PURPOSE: To make the cutting margin of a gear uniform as well as to enhance yield by roughly cutting the gear in such a way that both tooth faces are formed into crowning shapes which are fairly different between both the faces, and thereby cutting the faces into a finished form in such a way that they match the shapes of both the tooth faces respectively with the cutting margin kept uniform.

CONSTITUTION: When both the tooth faces 3 and 4 of each tooth 2 of a gear having a plurality of teeth 2 over its outer circumference, are formed into each tooth profile, that is, a crowning shape of the gear 1 where each center section 9 is swelled up for each face starting from one end face 7 toward the other end face 8, both the tooth faces 3b and 4b are roughly machined first into crowning shapes which are fairly different between both the tooth faces. And next, they are machined into a finished form with a cutting margin kept uniform in such a way that they match the shapes of both the tooth faces 3b and 4b respectively. After finish machining has been over, the gear 1 is heattreated, so that both the tooth faces 3 and 4 are made identical and symmetrical in a crowning shape by deformation due to heattreatment.