In a playback device for playing back a moving image recorded on a recording medium while executing an application recorded on the recording medium, to improve the use efficiency of a memory bus when combining the moving image with an image relating to the application. Whether or not to combine a background image, which is used as a background of GUI graphics such as a menu or a moving picture used by the application, is determined depending on whether the moving image covers the entire background image. If the moving image covers the background image, there is no need to combine the background image with the moving image. In this case, a memory bus allocated to the reading of the background image can be used for, for example, writing the moving image read from the recording medium onto a memory. Hence the memory bus bandwidth can be effectively used.