A computer functioning as three-dimensional (3D) computer aided design (3D-CAD) system executes the process for selecting a 3D model of a component from a library. The process includes a step for designating a category of a component; a step for displaying a menu for designating values of category-dependent items representing a specification of the component; a step for narrowing down, on the basis of the designated value, records of a database, in which each record for each component includes the items representing the specification; a step for extracting a possible value of an item with its value being undetermined and accordingly updating a choice(s) selectable via the menu; and a step for determining, to be a 3D model to be loaded from the library, the 3D model of the component uniquely determined after repeating the above-mentioned steps for narrowing-down, extracting and updating for one time or more.