PURPOSE: To provide a processing method for gears with accurate teeth thickness by measuring a center distance between a gear cutter and a master gear and introducing it to a numerical-control gear cutting machine for setting a cut depth of the gear cutter in cutting gears.

CONSTITUTION: One of a master gear M and its gear cutter (for example, a gear hob H) is fixed, the other end is slid so as to be meshed with each other without backlash, and then the center distance between the both is read with a scale 9 and a sensor 10. In a processing method for gears, which are processed Icy introducing the center distance to the controller of a numerical-control gear cutting machine and setting cut depth of the gear cutter, simple movement of a sliding shaft member 15 provides meshing of the gear cutter H with the master gear M without backlash so that the center distance between the gear cutter H and a gear C to be processed is automatically read by the numerical- control gear cutting machine and the depth cut by the gear cutter is determined accurately so as to allow processing of gears with correct teeth thickness.