A portable device registration system comprising: a portable device that is adapted to perform encrypted communication with a communication subject using the same encryption key, K-1; and a controller included in the communication subject, wherein the portable device registration system is adapted to register the portable device to the controller; wherein the controller is adapted to store identification information, VID-A, unique to the communication subject and a key generation logic, f, used to generate the encryption key K-1; wherein the portable device is adapted to store an encryption key generation code, SC-1, unique to the portable device and the encryption key, K-1, which is generated using the encryption key generation code, SC-1, stored in the portable device and the key generation logic, f, stored in the controller; wherein the controller is adapted to perform a registration process including writing the identification information, VID-A, to the portable device through wireless communication with the portable device, retrieving the encryption key generation code, SC-1, from the portable device through wireless communication with the portable device, generating an encryption key, K-1, that is the same as that of the portable device from the retrieved encryption key generation code, SC-1, using the key generation logic, f, stored in the controller, and storing the generated encryption key, K-1, in the controller; wherein the portable device registration system includes a deletion tool adapted to instruct the controller to transmit a deletion request signal to the portable device to delete the encryption key generation code, SC-1, from the portable device; and wherein the controller is adapted to transmit the deletion request signal to the portable device after receiving an instruction from the deletion tool, and wherein the portable device is adapted to delete the encryption key generation code, SC-1, from the portable device when receiving the deletion request signal, the portable device registration system further comprising a database that is adapted to save the identification information, VID-A, which is stored in the controller prior to shipment, with an additional registration encryption key, K-2, associated with the identification information, VID-A; and a supplemental portable device and a supplemental controller that are each adapted to store the identification information, VID-A, which is saved in the database, and the additional registration encryption key, K-2, saved in the database. a portable device that is adapted to perform encrypted communication with a communication subject using the same encryption key, K-1; and a controller included in the communication subject, wherein the portable device registration system is adapted to register the portable device to the controller; wherein the controller is adapted to store identification information, VID-A, unique to the communication subject and a key generation logic, f, used to generate the encryption key K-1; wherein the portable device is adapted to store an encryption key generation code, SC-1, unique to the portable device and the encryption key, K-1, which is generated using the encryption key generation code, SC-1, stored in the portable device and the key generation logic, f, stored in the controller; wherein the controller is adapted to perform a registration process including writing the identification information, VID-A, to the portable device through wireless communication with the portable device, retrieving the encryption key generation code, SC-1, from the portable device through wireless communication with the portable device, generating an encryption key, K-1, that is the same as that of the portable device from the retrieved encryption key generation code, SC-1, using the key generation logic, f, stored in the controller, and storing the generated encryption key, K-1, in the controller; wherein the portable device registration system includes a deletion tool adapted to instruct the controller to transmit a deletion request signal to the portable device to delete the encryption key generation code, SC-1, from the portable device; and wherein the controller is adapted to transmit the deletion request signal to the portable device after receiving an instruction from the deletion tool, and wherein the portable device is adapted to delete the encryption key generation code, SC-1, from the portable device when receiving the deletion request signal, the portable device registration system further comprising a database that is adapted to save the identification information, VID-A, which is stored in the controller prior to shipment, with an additional registration encryption key, K-2, associated with the identification information, VID-A; and a supplemental portable device and a supplemental controller that are each adapted to store the identification information, VID-A, which is saved in the database, and the additional registration encryption key, K-2, saved in the database.