PROBLEM TO BE SOLVED: To simplify description, a pre-processing such as check and input work of an original drawing and to exactly judge a connecting state between graphical factors. SOLUTION: A CAD-formed drawing in which state of system structure is expressed by using the graphical factors corresponding to each component of an object system is displayed (11). A boundary area as a closed area including all the graphical factors selected from the CAD-formed drawing is generated (12) by geometrical information of the selected graphical factors and preliminarily defined offset. The graphical factor a part of which is included in the generated boundary area is extracted as a connection candidate and the selected graphical factors and the extracted connection candidate are judged whether they are at the connecting state or not (14) by using restriction (13) for the CAD- formed drawing to be defined from semantics of the graphical factor corresponding to the extracted connection candidate.