A gear molding method for molding a plurality of plastic gears having a different number of ribs without changing costly gates uses a mold having a prescribed gear shape including a prescribed number of grooves substantially radially arranged in the mold. A prescribed number of gates is provided for pouring molten plastic into the mold. When a plastic gear is molded and separated from the mold, a prescribed number of grooves are additionally cut at a middle angular position between each of the pair of neighboring grooves without changing the gates. Then, another gear having increased number of ribs is molded using the same gates.