This paper proposes a reference model of CAD system generation, and describes its prototype implementation. The problems encountered in using CAD systems in industry involve complicated data handling and unsatisfied demands for domain knowledge because of the lack of a way of extracting and adopting it in the system. In the example domain of architecture, the authors have already defined domain-specific BDL (Building Design Language) for architecture experts to describe modelers of architectural structure in CAD systems by themselves. Moreover, the authors have developed a CAD system generator based on BDL descriptions. However, the different domain-specific languages required for individual domains create difficulty in developing various CAD system generators. The proposed reference model solves this problem by applying a common intermediate language based on the object model. Moreover, the model allows the creation of an integrated CAD system which contains multiple domains required by a field of industry. Its prototype implementation demonstrates its feasibility.