“Nudge theory,” an approach to influence people’s decision making, channels people’s behavior by designing environmental cues. We have been studying driving agents that encourage drivers to drive safely and make better behavioral choices for gently driving. Therefore, we attempted to apply a type of Nudge theory called default effect to driving agents. An example of the default effect is an instance wherein people need to make decisions immediately. They are more likely to follow other people’s opinions instead of considering the optimal choice. In this paper, we discuss the research outline of NAMIDA⁰, a multi-party interaction driving agent, and its application based on the Nudge theory.