When a key input unit or a touch panel is pressed, a control unit identifies the commanded function. Then, the control unit causes a human-body communication unit to start processing for establishing human-body communication with a portable device worn by a user. On receiving user information from the portable device, the control unit makes reference to an authentication table and determines whether or not there is an entry for the received user information therein. Further, the control unit determines whether or not use of the identified function, out of the functions corresponding to the received user information, is allowed. The control unit performs display on the touch panel, according to the result of the determination.