A relative movement trajectory of each convex tooth pin of a mating gear with respect to a concave-convex gear at the time when torque is transmitted between the mating gear and the concave-convex gear (nutation gear) may be expressed by a first linear axis, a second linear axis, a third linear axis, a fourth rotation axis, a fifth rotation axis and a sixth indexing axis. Then, a relative movement trajectory of each convex tooth pin of the mating gear, expressed by the first linear axis, the second linear axis, the third linear axis, the fifth rotation axis and the sixth indexing axis in the case where the fourth rotation axis is brought into coincidence with the sixth indexing axis, is calculated, and at least one of a disc-shaped workpiece and a working tool is moved on the basis of the calculated relative movement trajectory.