PURPOSE: When performing the gear cutting by means of NC gear hobbing machine, to eliminate the replacement of cutters and to enable the continuous working by arranging a plurality of different hob cutters on a hob arbor in parallel then shifting the cutter to the working position as required.

CONSTITUTION: Hob cutters 12, 13 having different features are fixed on a hob arbor 11 then secured through a fastening nut 14. Thereafter the hob arbor 11 is fixed on NC gear hobbing machine. Then a hob shaft slide 16 is moved by a hob shift motor 20 to position the hob cutter 13 in the center of hobbing 21 to perform the gear cutting. Then the hob cutter 12 is shifted to said position 21 by said slide 16 to perform the next gear cutting. With such structure, the multi- stage gear cutting can be performed efficiently without replacing the hob cutter.