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; and 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 for every image group.