A license administration device manages grant or denial of each optional function in a plurality of licensee devices. The licensee device stores key information encrypted with a cipher key so as to issue a license change request activating or restricting the predetermined optional function. Upon receiving a license change request restricting the predetermined optional function, the license administration device overwrites the key information of the licensee device with a default key. Subsequently, upon receiving a license change request activating the predetermined optional function, the license administration device applies an upgrade key to the key information of the licensee device. The default key or the upgrade key can be decrypted using a cipher key unique to the licensee device. The license administration device manages the licensed maximum for the predetermined optional function and reflects an increment or decrement to the licensing maximum by applying the default key or the upgrade key.