A navigation device (a vehicle-mounted navigation device 1) is connected, via a mobile communication network 3, to a server 5 by way of a telephone 2 connected thereto via cable 1a or radio 1b, and includes a communication control unit 12 for communicating with the server 5 by using the telephone 2 to measure parameter information about a command support status of the telephone 2 or a communication connection environment, and a main control unit 10 for transmitting the parameter information measured by the communication control unit 12 to an external storage medium 21 or the server 5, and for controlling subsequent communications according to the parameter information transmitted to the external storage medium 21 or the server 5.