1. A method for displaying a road map mesh in a form of bird's eye view on a display screen of a display unit, comprising: a) storing the road map mesh in a form of a plan view; b) placing a virtual viewpoint at an upper sky behind a predetermined position of display reference on the plan view formed road map mesh by a predetermined distance; c) looking down at the plan view formed road map mesh forward away from the predetermined point of display reference from said virtual viewpoint along a line of sight having an angle of field of view with respect to the predetermined point of display reference; d) setting the display screen on a plane perpendicular to the line of sight; e) extracting road map data from the plane view formed road map mesh corresponding to respective pixels on the display screen from the plan view formed road map mesh; and, f) drawing the bird's eye view of the plan view formed road map mesh on the display screen on the basis of the extracted road map data.