An authentication processing portion of an MFP requests user authentication to a server based on user information including at least a user ID input from a mobile terminal apparatus or an operation panel. The server has a user authentication portion which performs the user authentication and a UI instruction portion which specifies, when the user authentication succeeds, a UI image displayed on a display panel of the apparatus for operating the MFP depending on the user ID, and instructs the MFP to display the UI image on the apparatus. The MFP executes image output in accordance with a user operation received from the apparatus through the wireless communication portion in a state where the UI image is displayed on the apparatus.