High performance and robust fillet creation for complex support shape environment: High robustness is realized by the use of specifically developed own geometric engine for supporting fillet functions. Formability Fillet provides variety of functions. For example, 1. Fillet options such as variable radius, chord length specification, curve passing fillet, three tangent fillet and Gradation, etc. 2. Variable radius/ independent end conditions/ arbitrary stop position, etc. High flexibility is obtained by the fillet. Separated or combined running of fillet creation/edit of existing fillet/ merger of fillets to base shape are provided, which supports high quality and efficient fillet creation work.