Abstract: In a method of forming an offset configuration for a cutting tool which is used to machine a workpiece under the control of a numerical control device, both in the case where a cutting tool having first and second edges on both sides which have nose Rs, respectively, are used in such a manner that the cutting tool is moved horizontally and vertically with respect to a workpiece rotating, and the first edge is used when a machine configuration increases in vertical coordinate, and the second edge is used when a machining configuration decreases in vertical coordinate, and in the case where a cutting tool having first and second edges on both sides which have nose Rs, respectively, and provide a predetermined inclination angle .theta. is used in such a manner that the tool is moved horizontally and vertically with respect to a workpiece rotating, and the first edge is used when the inclination angle, in a vertical direction, of a machining configuration is smaller than the inclination angle .theta.