A designer-friendly CAD for a schematic design is one of the important topics of CAD studies. There were attractive preceding studies aiming to develop a CAD that intended to enable designers to have flexible design thinking and interactively manipulate representation models. This paper has the same goals of study, but focuses on the needs to support flexible and multi-aspect design thinking. Though designers normally hope to elaborate on their ideas using separate sets of representation models suitable for respective studies, a present CAD that is designed to build a single set 3D model, has limited its ability as a tool for a schematic design. Assuming this as the base concept, authors have studied to develop a prototype of a schematic design system, customizing AutoCAD R14J: Schematic Design System'98 (SDS'98). It has convenient utilities both for building separate sets of representation models and for integrating and reconciling those models to build a single consolidate model. This paper discusses the common procedures of schematic design studies, necessary functional features for SDS, a case study of the system use, and finally, the advantages and the disadvantages of the proposed system.