Changes of driver behavior by the rear-end collision prevention support system with road-to-vehicle communication, was evaluated on a public road. From a viewpoint of safety, “normative behavior” which the system certainly requires to a driver was defined as “deceleration behavior in a poor visibility section”, and it was compared between with-system and without-system conditions. As a result, behavioral changes of gas pedal release or speed decrease were observed in a part of participants. By analysis of driver’s individual characteristics, the result of behavioral changes could be interpreted as being due to driver’s situation awareness for the risk of “invisible objects”.