This invention realizes, with low cost, an image search apparatus which can quickly obtain adequate search results upon searching for document images which are identical or similar to a predetermined document image. To this end, an image search apparatus of this invention has the following arrangement. That is, an image search apparatus for searching for images similar to a query image, includes a region division unit (204, 209) which extracts a plurality of partial regions which form an image, a region feature extraction unit (205, 210) which calculates the number of partial regions and center of gravity positions, and a feature amount updating unit (206) which saves the calculated number of partial regions and center of gravity positions in an image region management DB (216) as an index. The image search apparatus loads partial regions which match the number of partial regions and center of gravity positions of a query image from the image region management DB (216) onto a memory, narrows down registered images on the basis of the loaded partial regions, and searches the narrowed-down registered images for images.