To provide a machining method of a resin gear with rib by which the machining manhour and the cost of materials can be reduced, and the durability of the gear can be improved by making the shape of a bottom of the gear formed to coincide with the shape of a tip of a mating gear to be engaged therewith.

In a machining method of a resin gear with rib where at least a surface part 9 including a tooth flank of a gear 3 is formed out of a resin, and the other part is formed out of a metallic material, the tooth shape of the gear 3 is roughly formed by the premolding, and then the tooth shape is finished by the machining such as hobbing, grinding or the like. The grinding work is performed by electro-depositing a grindstone 10a on the tooth flank of the mating gear to be engaged with the gear 3, and using the mating gear as a grinding tool 10.