Recently, the roundtable meeting, as a method for public participation, has received much attention. However, the number of committee members in the meeting is limited. So the complementary system becomes important. This paper aims to evaluate the public participation in the roundtable meeting by focusing particularly on the complementary system. A framework for assessing the public participation in roundtable meetings was presented. The case study was about a regional environmental restoration planning process named Sanbanze roundtable conference in Chiba, Japan. The results show that, by conducting of such an intensive participation process, especially the complementary system, a two-way communication between residents and the committee was built, and the conference received and adopted many suggestions from a wide range of public.