Abstract: A navigation system allows an automotive vehicle to travel along an optimum traffic lane of a roundabout in an efficient manner, and informs about an optimum outlet of the roundabout on the basis of an optimum travel route to the destination. When the judgment is made that there is a roundabout on the way to the destination on the basis of the optimum travel route calculated by the optimum travel route calculating section, the navigation system is adapted to detect a direction of an optimum output of the roundabout, to detect the number of traffic lanes of the roundabout, and to inform the driver about an optimum traffic lane in the roundabout.