5. The apparatus according to claim 4 , further comprising: a display count setting unit constructed to set, as the thumbnail configuration setting, a display count of the second thumbnail image to be displayed, wherein the thumbnail display unit selects pages or image elements to be displayed as the second thumbnail image according to the display count set by the display count setting unit, and displays a plurality of thumbnail images associated with the selected pages or image elements.
4. The apparatus according to claim 1 , wherein the second thumbnail image to be displayed further includes a plurality of thumbnail images associated with a plurality of pages or a plurality of image elements selected based on the thumbnail configuration setting and an arrangement order in turn from a page or an image element which neighbors the page or the image element that matches the retrieval condition.