An image search apparatus provides searching for a search-target image corresponding to an input image from among a plurality of search-target images. The image search apparatus includes a characteristic partial image detection unit and a search unit. The characteristic partial image detection unit detects a characteristic partial image of each search-target image based on a dissimilarity level of a partial image at a corresponding position among a plurality of search-target images. The search unit respectively calculates a level of coincidence between a characteristic partial image of each search-target image detected by the characteristic partial image detection unit and a partial image of an input image. The search unit further searches for a search-target image corresponding to an input image from among a plurality of search-target images based on the coincidence level.