PURPOSE: To machine with a high efficiency a curved surface which is excellent in the shape precision and symmetrical to the axis of revolution by modifying the original point of the locus, the radius and the position of the tool based on the results of the shape measurement, and executing the following machining by using the tool while executing a relative movement of the tool along the tool locus to be modified based on these modified values.

CONSTITUTION: The error ΔC when the tool original point is set, the mounting positional error ΔR of a tool 6, and the original point error Δθ of the tool position are obtained by a computation processing device 17 by using the errors of the shape of the surface to be machined which are measured by an electric displacement gauge and obtained from the shape of the surface to be machined. These values are received by a numerical control device 17, the tool original point, the tool mounting position and the original point of the tool position control are modified, and an objective shape of the surface to be machined can be obtained while an ideal tool locus being described by re-machining.