To provide a method for determining a tool axis vector, which method can properly determine the tool axis vector without carrying out the trial-and-error method even in the case of machining the attack angle side of a wing surface.

The tool axis vector is determined based on the state that the bottom surface or the side surface of the tool is brought into contact with the wing surface when the attack angle side of the wing surface is machined. Because the tool axis vector is determined based on the contacting state of the wing surface with the tool at the machining point, the interference of the tool with the wing surface can be prevented by determining the tool axis vector without carrying out the trial-and-error method. In addition, because the tool axis vector is determined based on the contacting state of the wing surface with the tool, the machining points where the tool interferes with the wing surface can be omitted, and machining paths capable of preventing over-cutting can be produced. Further, because the attack angle side and the other side of the wing are smoothly continued, the machining can be carried out without suddenly changing the posture of the tool even when the method for determining the tool axis vector has been changed for the attack angle side and the other side of the wing.