To easily find a desired keyword or image data to enhance operability for search by ranking the keywords or image data displayed at one hierarchy to display them, as the desired keyword or image data is hardly found when displayed at random if a large volume of the keywords or image data exist in one hierarchy, in the image search hierarchizing the keywords imparted to images preliminarily using a thesaurus dictionary.

Significance of the each keyword conformed with hierarchized classification is found for each classification. Sorting is carried out within the classification, based on the found significance, to display the keywords or the image data in a level of significance. Alternatively, the total number of the keywords consistent with the classification is found , and sorting is conducted based on the total number to display the registered keywords in the level of significance.