To realize safe autonomous evacuation, citizens should obtain well developed “mental model” for evacuation which includes appropriate perception mechanism to preserve flood risk and flexible “alternative set” for evacuation actions. Aiming at const meting well developed mental models which citizens' evacuation actions are determined based on, the paper develops a flood risk communication support system. Through communication among stakeholders assisted by the system, changes in flood risk perception and increase in the flexibility of the alternative plans of evacuation actions are observed in the experimental workshops in Kiyosu City, Aichi prefecture.