To provide a gear manufacturing method more excellent than a conventional gear manufacturing method.

This gear manufacturing method comprises a machining step to machine a stock gear formed of a ferrous material to form a gear, an austenitizing step to heat a tooth flank of the gear and keep it at the temperature not lower than the A1 transformation point to austenitize the structure of the ferrous material, a bainitizing step to control the temperature of the tooth flank so that the temperature of the tooth flank is within the first predetermined temperature range in which the bainitization of the ferrous material is advanced, and to bainitize at least a part of the tooth flank, and a nitriding step to nitride the tooth flank. This means that not the entire gear but only the tooth flank requiring the strength is heated to achieve the bainitization to strengthen the tooth flank, and the distortion of the gear caused by the bainitization can be suppressed to a minimum.