A framework of case-based design and its application to the mechanical design of induction motors are described. In the proposed framework, the use of multiple cases is essential in reducing the problem-solving complexity and ameliorating the knowledge acquisition bottleneck. Two subproblem generation processes are introduced: case-based reduction and goal-directed decomposition. In order to implement these processes effectively, a design model is introduced which maps requirement differences to the part of the design to be modified, and a decomposition algorithm is applied which takes into account the retrieval possibility and interaction occurrence. In a preliminary evaluation, the motor design system's performance was found to be as good as that of a human designer.<<ETX>>