In a communication-type navigation system for downloading map data according to the present invention, a reduction in the amount of map information to be transferred, correction of a position measured by a GPS, and delivery of advertisements are effected. In this system, a terminal 5 stores rough map data in advance. Then, when detailed map data is required, it is downloaded from a map data delivery center to the terminal 5. Further, together with the map data, GPS correction information is delivered to the terminal 5 from the map data delivery center 80. Still further, coupon information associated with an advertisement is displayed and an electronic mail on the coupon information is issued, by the map data delivery center.