An immobilizer device for a vehicle includes a key which has a transponder, an engine ECU, and an immobilizer ECU which receives a first identification information transmitted from the key and inputs the identification information to the engine ECU via a first identification information transmitting device. The immobilizer ECU includes a second identification information transmitting device which inputs second, different identification information to the engine ECU. The engine ECU includes a first and second identification information authentication devices which respectively authenticate the first identification information and the second identification information based on first and second comparison data set in the engine ECU. The engine ECU allows an engine to start when the first and second identification information are appropriately authenticated. The first identification information is based on random numbers generated by the engine ECU.