Abstract: In a CAD system, an electronic system is arranged by receiving an aid of a computer, and also a designing work of an architecture of this electronic system is carried out under the aid of the computer. An estimation with a high usability can be realized in high precision in an upstream stage, namely an earlier designating stage. The acquired design information is stored as know-how, and this stored know-how can be succeeded to the design information in a downstream stage. In this CAD system, a block diagram is edited by a block diagram input/editing unit, and this block diagram contains symbols indicative of independent functions, and lines used to connect these symbols. These symbols and lines are represented as the same design information. Both design information and parameter information may be applied to the symbols and the lines in a similar manner. Furthermore, the respective design information owns such a structure having a plurality of detailed level information with an architecture idea of a layer.