PURPOSE: To perform machining without changing setup for types of helical gears by engaging the first female type and the second female type with the outside of a male type which is linked with a main spindle and providing the first and the second connecting means for connecting the male type to the first female type or connecting the first female type to the second female type with detachment allowable.

CONSTITUTION: On the outer periphery of a male type 15 which is linked with a main spindle 11, the first helical protruded portion 15a is formed. Outside the protruded portion 15a, there is the first female type 16 provided with the first helical recessed portion 16a which interlocks with the protruded portion 15a. On the outer periphery of the first female type 16, the second female helical protruded portion 16b is formed. Outside the protruded portion 16b, there is the second female type 17 provided with the second helical recessed portion 17a which interlocks with the protruded portion 16b. The first connecting means for connecting the male type 15 to the first female type 16 with detachment allowable and the second connecting means for connecting the first female type 16 to the second female type 17 with detachment allowable are provided. It is thus possible to manufacture a helical gear along either the first or the second helical head depending upon the selection of the connecting means.