A navigation system includes: a map information acquiring unit for acquiring map information; an HOV lane decision unit for deciding whether an HOV lane is included in a road represented by the map information acquired by the map information acquiring unit or not; a road number processing unit for performing, when the HOV lane decision unit decides that the HOV lane is included, processing of adding information representing the HOV lane to a road number of the road including the HOV lane; and a display processing unit or a voice information unit for causing the road number passing through the processing by the road number processing unit to be displayed on the guide map or output in voice.