As described in this paper, we propose a Web-based system to support group idea generation. Our prior study created a method of group idea generation to develop each group member's idea through positive group communication. We introduce positive idea evaluation into the method to support its function. The system provides functions of a computerized paper and group communication that consists of idea evaluation and online chat. Using the computerized paper function, all members can input their ideas simultaneously: they can see the same paper. Furthermore, using the function of group communication, a member who evaluates an idea (i.e. evaluator) competes with others in finding good points of the evaluated member idea. Moreover, during a chat session, the evaluators then tell the evaluated member ways to improve it. While all members of a group concentrate on the screen, they can do group work for group idea generation. Results show that the proposed system is effective to support group idea generation: the group members were able to generate many ideas.