Communication route guidance system

In a communication route guidance system, data is transmitted and received between a information center and each of a plurality of mobile units mounted on moving bodies such as vehicles using communication. The information center has the latest road data. The information center prepares recommended route guidance data, in reference to said latest road data, for guiding the mobile unit from current position to a destination in respond to a request from the mobile unit. Said recommended route guidance data is divided into a plurality of segmental data which is formed to be usable independently in the mobile unit, and transmitted to the mobile unit, and then used for guiding the user of the mobile unit to the destination. The mobile unit has a road data similar to the road data in the information center and means for detecting whether or not the mobile unit can communicate with the information center. In a case where the mobile unit can not communicate with the information center, the mobile unit prepares a route guidance data in reference to the road data in the mobile unit, and guides the user of the mobile unit using said prepared route guidance data. In this way, it becomes possible to guide the user even in the case that the mobile unit can not communicate with the information center. Even in a case where a communication link is disrupted during transmission of route guidance data to the mobile unit, the mobile unit can effectively prepare whole route guidance data in combination with already-received route guidance data and additionally prepared route guidance data in reference to the road data in the mobile unit because of the already-received route guidance data is formed to be usable independently.