To provide a theft-prevention method for a vehicle in which the operation is not troublesome when loading and unloading a carriage with opening a door of a baggage room for the vehicle used for general purpose, in particular, for a transportation business, and capable of minimizing the modification of the vehicle when mounting it.

In the theft-prevention method for the vehicle having seat doors and a baggage room, when releasing the lock of the seat door and the baggage room door and operating the engine of the vehicle are inhibited, and/or the vehicle is unsuitably operated, a security function for commanding a warning is released, afterwards after the last door of the opened seat doors is closed and locked, the baggage door is closed and locked when a predermined time elapses the security is re-operated at the same time or after predetermined time elapse.