The designers often are required to derive ideas of the products satisfying requirements of users and market. To accomplish to derive good design, it is important to have much information for previous designs and collaborate with the other designers. At an early stage of design process, several designers have to derive ideas considering its evaluation in cooperation. In this stage, some existing methods to support thinking processes among several persons are useful. However, it is difficult to give a direction for discussion because a reasonable evaluation of ideas is difficult and it is also difficult for the evaluation to be accepted by the other designers. In this study, we propose a method to support generating various and effective ideas in conceptual design process. The ideas are mathematically defined to have factors of evaluation and features and numerically treated in these factors space. Data Envelopment Analysis (DEA) is applied for ideas having many factors of evaluation to derive reasonably a scalar value for evaluation result. DEA gives us a segment of many ideas and from this segment we can discuss a new idea. To support deriving a new idea, we have identified nonlinear mathematical model between factors of evaluation and features and optimization method was applied for the identified model. The proposed method is applied for the experiment and we could confirm the effectiveness of the proposed method.