Three-dimensional CAD systems contribute extensively to the detailed design processes of products. In detailed design work, designers are required not only to accurately define shapes of products but also to assign attribute information which is essential for the manufacturing process. However, it is extremely hard for inexperienced designers to determine optimum attribute values and design values. This paper introduces "Function Features" which give information on the function and role of each area of a designed part. The "Function Features" enables designers to acquire design attribute information and know-how which are related to a "Function Feature" by easy operations. A system based on the "Function Features" for the design of injection molds was developed and the results of simple design experiments confirmed the usefulness of the proposed method using "Function Features".