It is possible to present identification information of a sender in such a manner that the identification information is easily understood by a user. Included are: a wireless communication section (20) for carrying out data communication with the navigation device (50); and a line communication section (30) for carrying out data communication with the communication device (80), and an address sending section (22) for sending, to the navigation device (50) via the wireless communication section (20), first identification information for identifying the communication device (80); a position receiving section (26) for receiving position information from the communication device (80) via the line communication section (30); a position sending section (24) for sending the position information to the navigation device (50) via the wireless communication section (20); a message receiving section (32) for receiving a message from the navigation device (50) via the wireless communication section (20); an address adding section (34) for adding, to the message, second identification information for identifying the communication device (10); and a message sending section (36) for sending, to the communication device (80) via the line communication section (30), the message to which the second identification information is added.