It is important to design architecture to be steady throughout the evolution, or make the architecture to be the platform for product family. In order to design software arcitecture to have such characteristics we have to analyze the commonality and differences among requirements on potential software that are supposed to be developed on the architecture, and then design software architecture so as to accommodate the commonality and differences. In this paper, we propose an approach for architectural design in which we analyze the requirements on potential software in terms of the impact on the architecture, considering multiple quality attributes. We make case study on actual project that designed architecture for on-board system for ITS systems to examine the usefulness of the technique. We also apply the technique to the same architectural design problem to demonstrate that it is applicable to the real problem.