When a display map information is reduced to a specified scale for a wide area, items of congestion information are extracted which have a congestion level of “congested or busy”, and an overlap determination area is created for a congestion link of each item of extracted congestion information. The overlap determination area extends both transversely and longitudinally for a specified distance from the congestion link. Also, for each group of congestion information items having overlapping determination areas, an equal congestion level area is created by connecting the overlap determination areas and displayed in a color that corresponds to the congestion level. Equal congestion level areas are also created in the same manner for the congestion information items with congestion levels of “congested” and “not congested”, and displayed in different colors that correspond to their respective congestion levels.