Typical numeric data for specifying a shape of a first product having a typical size are stored in a storage portion. By an input portion (10), a size of a second product other than the typical size is input. A calculating portion (4) determines recommended numeric data for specifying a shape of the second product based on the size of the second product and the typical numeric data. By the input portion (10), furthermore, corrected numeric data for the recommended numeric data are input. The calculating portion (4) decides the validity of the corrected numeric data. In the case in which the corrected numeric data have the validity, the calculating portion (4) determines final numeric data for specifying the shape of the second product based on the recommended numeric data and the corrected numeric data. Based on the final numeric data, the shape of the second product is drawn by CAD software.