A traffic-congestion prevention system for preventing traffic congestion at a target location at a target time more certainly is provided. The traffic-congestion prevention system 10 includes a traffic state calculation unit 124 and a display control unit 16. The traffic state calculation unit 124 calculates a target traffic state that is a traffic state to be achieved at a location different from the target location in order to prevent traffic congestion at the target location at the target time. The display control unit 16 controls display means in such a way that the target traffic state at the location is displayed on the display means.