To suppress a continuous use of vehicle after an illicit act such as a theft of a vehicle or a theft of an electronic device such as an ECU.

In this system, an engine can be started in established states of authentications of validity of the electronic devices (ECU 1 to 3, for instance). The system is provided with an exclusive tool 12 capable of changing non-established states of the authentications into the established states. The system has a flag 31 turned on when a plurality of electronic devices (ECU 1 to 5, for instance) connected by an in-vehicle LAN 14 detects the illicit act to the vehicle 13 or when an intention display of a vehicle possessor is provided. In the ON state of the flag 13, the non-established states can not be changed into the established states by the exclusive tool 12.