A server issues a service key for using a designated vehicle and a plurality of one-time authentication keys based on a request from the mobile terminal, and distributes the one-time authentication key to the mobile terminal. The one-time authentication key is a disposable authentication key generated based on the service key, and has an expiration date. The one-time authentication key is consumed when the vehicular device authenticates the mobile terminal as a communication partner. The mobile terminal replaces the one-time authentication key stored in the mobile terminal at any time.