A method for displaying a graphic user interface at a control apparatus connected to a local network, the method comprising: displaying a place selection menu for selecting a place in which at least one multimedia device is located; displaying, upon selection from the place selection menu, a player selection menu including a player list of at least one player (160, 170, 180) located in the selected place; displaying upon selection a player from the player list of the player selection menu, a source selection menu including a source list of at least one source (130, 140, 150) capable of outputting contents to the selected player while displaying at least one locking menu for setting a locking function corresponding to each of the selected player and the at least one source in the source list; and displaying a list of contents available from a source (130, 140, 150) selected from the source list of the source selection menu; and controlling connection between the source (130, 140, 150) and the player (160, 170, 180), upon selection of the at least one source selection menu, wherein the locking function includes a control locking function for disabling at least one of the player (160, 170, 180) and the source from being controlled wherein if the control locking function of a player (160, 170, 180) among the at least one player (160, 170, 180) in the player list is already locked by another control apparatus when the player selection menu is displayed, the player (160, 170, 180) whose control locking function is locked is displayed as being unavailable for selection in the player list, and wherein if the control locking function of a source (130, 140, 150) among the at least one source (130, 140, 150) in the source list is already locked by another control apparatus when the source selection menu is displayed, the source (130, 140, 150) whose control locking function is locked is displayed as being unavailable for unlocking the control locking function in the locking menu. displaying a place selection menu for selecting a place in which at least one multimedia device is located; displaying, upon selection from the place selection menu, a player selection menu including a player list of at least one player (160, 170, 180) located in the selected place; displaying upon selection a player from the player list of the player selection menu, a source selection menu including a source list of at least one source (130, 140, 150) capable of outputting contents to the selected player while displaying at least one locking menu for setting a locking function corresponding to each of the selected player and the at least one source in the source list; and displaying a list of contents available from a source (130, 140, 150) selected from the source list of the source selection menu; and controlling connection between the source (130, 140, 150) and the player (160, 170, 180), upon selection of the at least one source selection menu, wherein the locking function includes a control locking function for disabling at least one of the player (160, 170, 180) and the source from being controlled wherein if the control locking function of a player (160, 170, 180) among the at least one player (160, 170, 180) in the player list is already locked by another control apparatus when the player selection menu is displayed, the player (160, 170, 180) whose control locking function is locked is displayed as being unavailable for selection in the player list, and wherein if the control locking function of a source (130, 140, 150) among the at least one source (130, 140, 150) in the source list is already locked by another control apparatus when the source selection menu is displayed, the source (130, 140, 150) whose control locking function is locked is displayed as being unavailable for unlocking the control locking function in the locking menu.