1. An image retrieval system, comprising: a characteristic descriptor producing unit for extracting a plurality of image characteristic values from pieces of input image data and producing a characteristic descriptor for each piece of input image data; an image information storing unit for storing the characteristic descriptors produced in the characteristic descriptor producing unit while holding the correspondence of each characteristic descriptor to one piece of input image data; an attribute list producing unit for producing an attribute list according to a piece of attribute information attached to each piece of input image data; and an image retrieving unit for receiving a first retrieval condition relating to attribute information, searching the attribute list produced in the attribute list producing unit for one piece of attribute information conforming to the first retrieval condition, outputting the piece of attribute information conforming to the first retrieval condition, receiving a second retrieval condition relating to a characteristic descriptor, searching the image information storing unit for one piece of image data conforming to the second retrieval condition, and outputting the piece of image data conforming to the second retrieval condition.