A communication system and a comparison method for securing a communication path for a legitimate user via a terminal apparatus (“TA”). A vehicle-mounted communication device (“VMCD”) transmits a device ID identifying the VMCD to a TA, acquires a terminal ID from the TA, and transmits the device ID and the terminal ID acquired from the TA to a central apparatus. The TA transmits a terminal ID identifying the TA to the VMCD, acquires a device ID from the VMCD, and transmits the terminal ID and the device ID acquired from the VMCD to the central apparatus. The central apparatus receives a device ID and a terminal ID transmitted from the VMCD and a device ID and a terminal ID transmitted from the TA, and compares the device ID and the terminal ID received from the VMCD with the device ID and the terminal ID received from the TA.