An immobilizer ECU generates an encryption key using key generating logic, from a SEED code included in an ID code signal sent from an electronic key, and registers the encryption key to the immobilizer ECU. The immobilizer ECU receives an instruction from a registration and deletion tool and sends, to the electronic key, a deletion request signal that requests the deletion of the SEED code. The electronic key deletes the SEED code from the electronic key if a deletion request signal has been received.