Attractive products are changed significantly by requirement definition and conceptual design phase. Quality of product concept, which is result of these phases, depends heavily on creativity of designer ore development team. Therefore, it is difficulty that computer-aided system supports a creative and inventive thinking process, to search a creative design solution. To overcome its difficulty, we developed the synthesis approach which combined the Particle Swarm Optimization (PSO) algorithm and the Particles Method of Unified Structured Inventive Thinking (USIT) for supporting to top-down thinking in problem solving process, and confirmed the validity of this approach. In this paper, to improve the mechanical function database, we introduce Pahl & Bietz's system approaches, and a new combination of function is generated by this approach automatically. The validity of this approach is discussed via the case problem.