This paper proposes a new Simultaneous Design Method that is called Global Relations Diagram of function and demarcation (G-RD). When enterprises aim to perform BPR, not only the breakdown of business functions but also the design of the relations between businesses is required. Generally, BPR projects focus on the breakdown of business functions, but the relations between businesses are not fully designed by the conventional design method, Sequential Design Method, in many cases. In order to solve these problems, the modeling approach which details not only the business functions but also the relations simultaneously is required. This paper introduces some case studies which applies this Simultaneous Design Method to the BPR projects, and confirms the effectiveness of this Method utilizing G-RD.