An electronic key registration method for registering a first electronic key, which is capable of controlling a communication subject, to a controller of the communication subject, the electronic key registration method comprising: an initial production step of storing identification information (VID-A) unique to the communication subject in the controller, and storing, in the first electronic key, an encryption key generation code (SC-1) unique to the first electronic key and an encryption key (K-1) that is used to verify the first electronic key; and an initial registration step of writing the identification information (VID-A) stored in the controller to the first electronic key, obtaining the encryption key generation code (SC-1) from the first electronic key, generating the encryption key (K-1) with an encryption key generation logic (f) that uses the encryption key generation code (SC-1), registering the first electronic key to the controller by storing the encryption key (K-1) in the controller, storing encryption key information (SC-1, K1) related to the encryption key (K-1) in a database in association with the identification information (VID-A), and after the registering the first electronic key to the controller, deleting the encryption key generation code (SC-1) from the first electronic key. an initial production step of storing identification information (VID-A) unique to the communication subject in the controller, and storing, in the first electronic key, an encryption key generation code (SC-1) unique to the first electronic key and an encryption key (K-1) that is used to verify the first electronic key; and storing identification information (VID-A) unique to the communication subject in the controller, and storing, in the first electronic key, an encryption key generation code (SC-1) unique to the first electronic key and an encryption key (K-1) that is used to verify the first electronic key; and an initial registration step of writing the identification information (VID-A) stored in the controller to the first electronic key, obtaining the encryption key generation code (SC-1) from the first electronic key, generating the encryption key (K-1) with an encryption key generation logic (f) that uses the encryption key generation code (SC-1), registering the first electronic key to the controller by storing the encryption key (K-1) in the controller, storing encryption key information (SC-1, K1) related to the encryption key (K-1) in a database in association with the identification information (VID-A), and after the registering the first electronic key to the controller, deleting the encryption key generation code (SC-1) from the first electronic key. writing the identification information (VID-A) stored in the controller to the first electronic key, obtaining the encryption key generation code (SC-1) from the first electronic key, generating the encryption key (K-1) with an encryption key generation logic (f) that uses the encryption key generation code (SC-1), registering the first electronic key to the controller by storing the encryption key (K-1) in the controller, storing encryption key information (SC-1, K1) related to the encryption key (K-1) in a database in association with the identification information (VID-A), and after the registering the first electronic key to the controller, deleting the encryption key generation code (SC-1) from the first electronic key.