1. A navigation system for an automotive vehicle, comprising: a storing section that stores therein a travel history of the vehicle which is made correspondent with a road map information; a calculating section that calculates a degree of familiarity with one of predetermined regions for each of the predetermined regions in the road map information on the basis of the travel history of the vehicle and its corresponding road map information; and an information producing section that produces the road map information in accordance with the degree of familiarity with the one of the predetermined regions calculated by the calculating section.