PURPOSE: To make it possible to perform gear cutting of racks whose each tooth form is different by degrees efficiently and moreover with accuracy by using a polygonal gear cutter whose sides are formed in rack cutter whose respective tooth forms are different.

CONSTITUTION: Rack cutters 18 through 21 having respective tooth forms meeting conditions corresponding to tooth forms of workpieces to be cut are formed on each side of the body 17 of a gear cutter 16. The rack cutter to be used is indexed and rotated as to be opposed to the specified position of a workpiece to perform rack cutting. Another rack cutter to be used for another ruck cutting is indexed and rotated as to be opposed to the specified position of another workpiece. The continuous performing of these manners in order allows the gear cutter to finish racks whose each tooth form is different by degrees.