There is provided a display device that enables to present an image on its screen at a desired resolution, in response to an operation by a user and on the basis of an image signal, even when the image signal is obtained from image data from which a resolution is not directly determinable. When image data from which the resolution is undeterminable is inputted, the display device presents thereon data input window that prompts the user to input desired values of the resolution and pixel clock at which the image is to be presented. The user then inputs his/her desired values of the resolution and pixel clock through the image-data input screen. Using the inputted values of the resolution and pixel clock, the display device presents the image on its screen based on the image data that is not normally supported by the display device.