Each of ECUs constituting a system of a vehicle is registered with authentication IDs of other ECUs. The each of ECUs determines whether the other ECUs are regular by comparing the registered IDs with authentication IDs newly obtained from the other ECUs when the system is started. When a certain ECU within the other ECUs is determined to be not regular, the certain ECU is prohibited from being used in this system. Further, when a new ECU is substituted or added, a terminal confirms whether the new ECU is unused in another vehicle and is thereby enabled to be usable by transmitting an authentication ID of the new ECU to a management center. When the new ECU is confirmed to be enabled to be usable, authentication IDs registered in the respective ECUs are updated.