A display apparatus comprising: a display device; an image processor which is configured to process an image to display the image on the display device; a communication unit which is configured to communicate with a first external device in which content data are stored and a second external device in which an application for processing the content data is stored; and a controller which is configured to control the communication unit to communicate with the first and second external devices and display a user interface, UI, images corresponding to the content data and to the application on the display device, and controls a processing operation of the application with respect to the content data through the UI images; wherein the UI images comprises a first UI image corresponding to the first external device and a second UI image corresponding to the second external device, and the controller is configured to control the processing operation of the content data according to an input from the first UI image and the second UI image, the apparatus characterized in that the first UI image and the second UI image correspond to UI images provided by the first and second external devices (210, 220), respectively, and wherein the first UI image comprises a list of the content data stored in the first external device, the second UI image comprises an execution view of the application of the second external device, and the controller is configured to control the processing operation of the application with respect to first said content data from the list, when the input from the first and second UI images (321, 322) comprises a drag and drop of the first content data to a said execution view of the application, and the controller is configured to control the first external device to transmit the first content data to the second external device, and the controller is further configured to control the second external device to process the first content data by the application executed by the second external device and wherein the controller is configured to transmit a control signal to the second external device in response to the receiving of an input to manipulate a processing operation of the application through the second UI image, and to control the second external device to operate the application corresponding to the control signal. a display device; an image processor which is configured to process an image to display the image on the display device; a communication unit which is configured to communicate with a first external device in which content data are stored and a second external device in which an application for processing the content data is stored; and a controller which is configured to control the communication unit to communicate with the first and second external devices and display a user interface, UI, images corresponding to the content data and to the application on the display device, and controls a processing operation of the application with respect to the content data through the UI images; wherein the UI images comprises a first UI image corresponding to the first external device and a second UI image corresponding to the second external device, and the controller is configured to control the processing operation of the content data according to an input from the first UI image and the second UI image, the apparatus characterized in that the first UI image and the second UI image correspond to UI images provided by the first and second external devices (210, 220), respectively, and wherein the first UI image comprises a list of the content data stored in the first external device, the second UI image comprises an execution view of the application of the second external device, and the controller is configured to control the processing operation of the application with respect to first said content data from the list, when the input from the first and second UI images (321, 322) comprises a drag and drop of the first content data to a said execution view of the application, and the controller is configured to control the first external device to transmit the first content data to the second external device, and the controller is further configured to control the second external device to process the first content data by the application executed by the second external device and