A transmission side transmits the road shape data of an object road 101 to be transmitted, and the branch shape data of a branch 20 intersecting with or branching from the object road 101. A reception side specifies the object road 101 on its own digital map with reference to the branch 20. In this method, the information indicating the shape of a branch or an intersection, which is liable to be erroneously identified, is transmitted as branch shape data to the reception side, so that the reception side can avoid the erroneous location identification. The branch shape 20 makes it possible to discriminate the object road 101 and a parallel road and to discriminate a discrepancy in the longitudinal direction of the object road 101, so that the erroneous location identification to the parallel road or the erroneous location identification in the longitudinal direction of the object road 101 can also be prevented.
