In this paper, we propose the framework of an integrated design system as a CAD system of a new concept that can incorporate the design information. Current CAD systems are powerful in representing the shape of a product with solid models but cannot provide the design information that is used or created in designing the product. Therefore an integrated design system is proposed to enable the storage and usage of the design information in addition to the shape manipulation. In order to represent the design information, we define element object that represents design element such as a part, a sub-assembly or an assembly by using object-oriented methodology. The element object carries various design information such as design parameters, documents, catalogues, functions, and behaviors as well as shapes. By using the stored information, the system can provide a designer with some functions to assist design activity such as interrogating necessary information, setting design parameters and goals, and constructing constraints among design elements. A mailing system is also constructed among element objects to assist a collaborative design. In addition, an evolutionary design method using genetic algorithms is realized within the proposed framework.