PURPOSE: To align gears with higher precision for a short period of time by making use of a gear processing tool including in a body a guide gear of the same shape as a blade tip edge of a processing blade part of a finishing tool on the extension of a tooth shape of said processing blade part upon finishing a roughly processed gear.

CONSTITUTION: To finish a roughly finished gear having a margin for finishing and not yet processed while applying a processing blade part of a gear finishing tool to said roughly processed gear, a gear processing tool is employed, which has in a body a guide tooth part 5 of the same tooth shape as a blade tip end of a hob cutting blade part 6 composed of rack cutting blades 2, 2... on the extension of a tooth of said hob cutting blade part. Hereby, a guide tooth part 5 is aligned with a lower cutting tooth 11 of a roughly finished gear 10 for positioning an angle of the tooth shape of the lower cutting tooth 11 with respect to the tooth part 5. Then, the cutting blade part 6 is shifted to the position of the lower cutting tooth 11 while keeping a relationship between tooth shape angles of said cutting blade part and the lower cutting blade 11, and furthermore nothed for a marging for finishing. Hereby, high precision tooth alignment can be effected for a short period of time for finishing the gear in concern.