To easily and accurately generate the CAD data of a structure in a short time.

In a step S1, the respective curved surfaces of a roof for instance are indicated by plural curves as the structure and data for indicating a numerical formula for expressing the curves are generated. Then, in the step S2, the three-dimensional coordinate value data of respective points on the respective curves are obtained based on the numerical formula indicated by the data generated in the step S1. Then, in the step S3, the three-dimensional CAD data of a DXF form are generated by the coordinate value data obtained in the step S2. By the CAD data, images in the case of viewing the roof from various angles are displayed on the screen of a monitor or printed by using a CAD software on the market for instance (step S4), and by the output results, the construction execution schedule of the structure for instance is planned without referring to the model of the structure as conventional way (step S5).