1. An image display apparatus comprising: an image classification unit configured to classify image data to which attribute information is added into groups based on the attribute information so as to generate one or more image groups; a display control unit configured to display, on a display device, a list of a plurality of thumbnail images of the image data included in each of the image groups generated by the image classification unit, in a manner in which the plurality of thumbnail images are piled up into a bundle of images for every image group; and a direction receiving unit configured to receive a selection for one of the image groups generated by the image classification unit; wherein the display control unit is configured to: acquire a predetermined number of sheets of image data from the selected image group received by the direction receiving unit; display, on the display device, the sheets of image data as a background image in which the sheets of image data are arranged; display each of the bundle of images on a belt-shaped region that is distinguishable from the background image; and display, together with the sheets of image data arranged as the background image, a thumbnail image of the image data included in the selected image group on a top surface of a bundle of the selected image group.