PURPOSE: To make it possible to perform a high speed gear cutting operation by a small lead pinion to eliminate the need for changing a helical guide by adding a reciprocating oscillation to a cutter spindle in synchronism with an axial reciprocating motion by change gears, and adding a generating rotary motion by a differential gear.

CONSTITUTION: A gear 9 is reciprocatively oscillated from a shaft of a segment 3 through change gear trains 11W17 in synchronism with an axial reciprocating motion of a cutter spindle 2, and the oscillating motion is boosted by a planet gear supporting frame 20 and a planet gear 21 to be transferred to a gear 8 to reciprocatively oscillate the cutter spindle 2. The cutter spindle 2 is axially moved by the segment 3 to be rotated by a gear 8. When a certain ratio of an axial reciprocating stroke S to a reciprocating oscillation R is selected, it allows the cutter spindle 2 to make a screw motion in which a lead L is equal to a lead of tooth trace of a helical pinion cutter 1 of a diameter d. In order to add a generating rotary motion to the cutter spindle, an internal gear 10 is connected to a master worm wheel, and the cutter spindle is rotated at a rate of speed ratio of the number of teeth of the helical pinion cutter 1 to the number of teeth of a face gear 7 to be gear-cut by using an indexing change gear 19.