A control device (1) of a gear processing machine has a bus (51) that communicates by directly connecting between a tool axis controller (22) and a workpiece axis controller (12), and, in this control device, the position of a tool axis (40) that is detected by a tool axis position detection sensor (25) is supplied to a workpiece axis controller via a bus, an upper controller (10) supplies a predetermined synchronization ratio and a superimposition command for applying a twisting operation to a workpiece axis controller, and the workpiece axis controller adds a value that is generated by multiplying the position of the tool axis that is supplied via the bus, by the synchronization ratio, and the superimposition command, and generates a motion command for a workpiece axis (30).