To make a control point directly usable as input data by using a master set as a control point set for the next iteration if the control point set is converged and using a right slave set or a left slave set as a control point set for the next iteration if the right or left slave set is converged.

A path selecting part 90 analyzes a control point from LR and EP operating parts to decide whether to produce output data, what to do with feedback and the last stop. A multiplexer 70 controls the input source of the two operating parts and makes the LR and EP operating parts receive feedback data only from the part 90, except that the first input data comes from an input control point register 50. An output control point register 60 stores curve output data. A segment producing part 40 further handles the output data and linearly simulates a Bezier curve that is divided and is converged on a straight line.