The present invention reduces the incident resolution judgment processing load on a traffic information center included in an incident detection system. When an incident occurs, the traffic information center generates an incident resolution judgment condition, which is to be used by each vehicle to judge whether the incident is resolved, and transmits the generated incident resolution judgment condition to each vehicle. Each vehicle judges in accordance with its travel history information and the received incident resolution judgment condition whether the incident is resolved. When the incident is judged to be resolved, each vehicle notifies the traffic information center that the incident is resolved. In accordance with incident resolution detection results produced by a plurality of vehicles, the traffic information center forms a final judgment to indicate that the incident is actually resolved, and notifies each vehicle of incident resolution.