1. A navigation system for a vehicle, the system comprising: a displaying means having a display screen; a detecting means for detecting a present position and a heading direction of the vehicle; a storing means for storing road map data for displaying a road map including a road, name of a road that is indicated by a plurality of line segments; a display managing means for reading road map data from the storing means based on the detected present position, and displaying a peripheral road map and a vehicle mark indicating the present position and the heading direction of the vehicle such that the heading direction is shown upwardly in the display screen, wherein the display managing means includes: an angle calculating means for calculating, relative to a traveling road that the vehicle presently travels on, an intersecting angle of an extending direction of a cross road intersecting with the traveling road at an intersection; a search area designating means for designating a search area shaped of a sector centering on the intersection to include the extending direction of the cross road; an intersecting point retrieving means for determining and retrieving an arc intersecting point of the cross road at an outer circumference arc of the designated search area; and a display position determining means for determining a display position of a road name of the cross road based on a line segment between the intersection and the retrieved arc intersecting point.