To reduce throughput required for retrieval in an image retrieval system having a partial matching function.

This image retrieval device for calculating similarity between an image to be retrieved and an image as a retrieval condition to execute image retrieval has: an image processing part 102 for acquiring the image to be retrieved, extracting a partial image showing a portion of the acquired image, generating numerical string information on the basis of the partial image, and generating subtraction numerical string information by excluding the numerical string information generated on the basis of the partial image from the numerical string information generated on the basis of the image to be retrieved; and a similarity calculating part 103 for calculating the similarity on the basis of the generated subtraction numerical string information.

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