To make changeable an arithmetic method used to convert NC data into graphic data.

In the CAD/CAM device 10 an arithmetic method storage part 5 stores arithmetic methods such as a center coordinate position priority method, an end-point coordinate position priority method, a horizontal and vertical line coordinate position priority method, a radius priority method, and an angle priority method and an NC data acquisition part 1 acquires NC data, and an operator selects one or plural arithmetic methods out of the methods stored in the arithmetic method storage part 5 by using an arithmetic method selection part 6, a graphic data generation part 2 generates graphic data by the arithmetic method selected by the operator, a display part 3 displays an image of the graphic data, and an NC data generation part 4 generates NC data from the graphic data.