It can confirm candidates of functional parts that can be selected as a function restriction release target, and can select the functional parts of the function restriction release target prior to receiving a release code. A mobile terminal sends registration information, which includes a MAC address acquired from a multifunction device, to a server. An authentication process of the compound device is performed in the server. After that, an additional function selection screen is displayed in the mobile terminal based on the data sent from the server. The user controls the mobile terminal to select additional functions and to send additional function selection information, and a payment process is performed for the server. The release code is sent from the server to the mobile terminal. The multifunction device releases the function restriction of the corresponded functional parts based on the release code.