A mobile body-mounted communication device mounted in a mobile body such as a vehicle and making difficult the long-time tracking of the moving path of the mobile body. The mobile body-mounted communication device mounted in a mobile body and used for transmitting/receiving packet information is characterized by comprising a borrowing address acquiring section for acquiring lending addresses as borrowed addresses from an address management device managing lending addresses, a borrowing time information acquiring section for acquiring information representing predetermined times during which the borrowing addresses can be used from the address management device, and a transmitting section for transmitting packet information including information on a borrowing address out of the borrowing addresses and the mobile body during the predetermined borrowing times determined for the borrowing addresses.