A vehicle is provided with an identification information memory in which identification information of the vehicle is memorized, and a transmitter for transmitting the identification information. A portable terminal is provided with a receiver for receiving the identification information transmitted from the transmitter, a registration information memory in which identification information of a ridable vehicle is memorized as registration information in advance, and a controller for executing authentication between the identification information and the registration information and executing a warning processing when a result of authentication shows inconsistency.