NUMERICAL CONTROL APPARATUS AND NUMERICAL CONTROL METHOD

A numerical control apparatus includes: a curvature radius calculating portion which calculates a first radius ra which is a radius of a passage arc C passing through three points of a start point Ps, an object point Pt, and an end point Pe as a curvature radius R at the object point Pt; a point sequence evaluating portion which calculates a chord error E to the passage arc C and compares the calculated chord error E and a previously defined permissible error; and a curvature radius correcting portion which calculates a second radius which is a radius of an arc in which a chord error with a front line segment and a rear line segment is the permissible error or less when the calculated chord error E exceeds the permissible error and corrects a curvature radius at the object point Pt to the second radius.