Patent ID: 8207817

Claim:
An electronic key system comprising: an authentication portion which checks, using two-way communication, a key code stored in an electronic key against a key code stored in a lock device that locks an entrance to a predetermined space; and a controller which allows an unlocking operation of the lock device when, according to the authentication portion, the key code stored in the electronic key matches the key code stored in the lock device, wherein the key code includes an identification code unique to the electronic key and a property code indicative of a property of the electronic key, wherein the property code is a code which alone indicates whether the electronic key is a master key that was registered in advance at the time of shipping and whether the electronic key is an additional key that was newly registered after shipping, wherein the lock device erases at least one key code that includes a predetermined property code, from among the key codes stored in the lock device, when a predetermined operation is performed, and wherein the lock device erases only key codes that include a property code indicating that the electronic key is an additional key from among the key codes stored in the lock device.