1. An information processing device comprising: an image display unit configured to display one or more main images within a main area in a screen and one or more sub images within a sub area in the screen, each of the sub images being associated with one of the main images, whereby a user is permitted to select the sub images in order to invoke the associated main images and at least one of the main images includes representations of one or more of the sub images that are not associated with such at least one main image; and a display control section configured to display respective ones of the main images on the main area of the screen in response to the user selecting the associated ones of the sub images such that: (i) as the user sequentially adds a respective one of the sub images to a series of selected sub images, the main image associated with such added sub image is sequentially displayed on the main area of the screen, thereby replacing another main image in sequence, and all of the respective sub images in the series are simultaneously displayed in order of selection in the sub area of the screen, and (ii) when the user re-selects one of the sub images already in the series of selected sub images by selecting the one of the sub images that is displayed in the order of selection in the sub area of the screen, the main image associated with the re-selected sub image is again displayed on the main area of the screen, thereby replacing another of the main images, and all sub images in the series that had been selected after the re-selected sub image had been initially selected are deleted from the sub area of the screen thereby truncating the series.