The demands of users are diverse. In design, a derivation of exact design solution is important for responding to the diverse demands of users. It is necessary for achieving the derivation of exact design solution to properly connect the early to the late process of design. In the early process of design, the demands of users are considered and the structural model is often used. On the other hand, in the late process of design, a design solution responding to the demands of users is derived and the mathematical model is often used. In the conventional studies, the design methods that contribute to each model building have been proposed. However, a design method that integrates the building of both models has not been proposed. Firstly, the Integrated Design Model was paid attention to, and the Integrated QFD, to which the ISM method was introduced, was proposed as the structural model building method that reflects the features of the Integrated Design Model. Secondly, the design factor selection method was proposed based on the Integrated QFD. Thirdly, a design method that has an ability to integrate the building of both models was proposed using the Integrated QFD and the design factor selection method. Finally, the effectiveness of the proposed design method was confirmed by applying to a driver seat designs. Thus, this study represented a design method that effectively promoted the early and late process of design and indicated the possibility of deriving exact design solution by using the Integrated Design Model.