A mobile body information system comprises a center system and a vehicle-mounted terminal device. The vehicle-mounted terminal device is configured to determine a density of communication areas of narrow area wireless base stations along a travel route of a vehicle based on a current position of the vehicle and installation data of the narrow area wireless base stations. When the density of communication areas is high, the vehicle-mounted terminal device is configured to recommend to a user a divided download format in which the information is intermittently distributed through a plurality of the narrow area wireless base stations while the vehicle is travelling. When the density of the communication areas is low, the vehicle-mounted terminal device is configured to recommend a batch download format in which the information is distributed through one of the narrow area wireless base stations while the vehicle remains in one communication area.