PURPOSE: To shorten a span of profiling time for a cylindrical cam groove or the like by setting plural pieces of point coordinates on the circumference of a model with a position on a rotation axis and its turning angle, using a line, connecting these coordinates, as a potential line for profiling, and setting each optional range on the circumference down to a machining area.

CONSTITUTION: Each of point coordinates (x1, θ1) shows a point P1 on the circumference of a model 6 whose position on an X-axis is a point x1 and that on a rotation axis A is an angle θ1, and point P2, P3, P4 and so on are set to the same too. These points P1, P2, P3, P4, P5 are designated and a positive potential line LP is set on the circumference of the model 6 along a cylindrical cam groove, and then points P6, P7, P8, P9, P10 are connected together, thereby setting a negative potential line LN there. When a stylus 5 profiles an X-axis in the positive direction, a controller monitors the negative potential line LN, and when exceeding the potential line LP, it imposes a pick feed on an A-axis direction, and when the X-axis is profiled in the negative direction, it imposes the pick feed on the A axis direction as well when exceeding the potential line LN.