1. An image search apparatus for searching for a detection-target image, comprising: a detection device for finding a detection-target image portion, based upon an evaluation value indicating degree of detection-target likeliness, in an image subjected to detection; a storage device for storing information concerning the detection-target image portion that has been found by said detection device; a determination device for determining whether a number of detection-target image portions that have been found by said detection device is equal to or greater than a prescribed number; and an erasing device, responsive to a determination by said determination device that the number is equal to or greater than the prescribed number, for erasing detection-target image portions, which have been stored in the storage device, in order of increasing reference value that is based upon a prescribed criterion in such a manner that the number of detection-target image portions that have been found by said detection device will fall below the prescribed number.