5. A non-transitory computer-readable recording medium having recorded thereon a program that includes a command for causing a computer to execute the steps of: receiving data comprising a search condition, wherein the search condition comprises a document designated by a person doing a search; extracting diagram information from image data of diagrams dotted throughout data of the designated document, wherein the diagram information comprises a feature amount of a diagram included in the designated document, an appearance order of the diagram, and an appearance position of the diagram; comparing the diagram information extracted in the step (b) with diagram information of a registered document that is registered in advance, specifying a diagram that is similar in the designated document and the registered document, estimating lines that are similar between the designated document and the registered document; and taking a count of the estimated lines as an estimated a similarity between the data and the registered document; and generating a search result capable of specifying a similar document that is related to the data, based on the estimated similarity; and acquiring data of the registered document from a database in which the registered document is stored, extracting diagram information from the acquired data of the registered document, and updating the contents of a diagram information database storing diagram information of the registered document, using the extracted diagram information.
5. A non-transitory computer-readable recording medium having recorded thereon a program that includes a command for causing a computer to execute the steps of: receiving data comprising a search condition, wherein the search condition comprises a document designated by a person doing a search; extracting diagram information from image data of diagrams dotted throughout data of the designated document, wherein the diagram information comprises a feature amount of a diagram included in the designated document, an appearance order of the diagram, and an appearance position of the diagram; comparing the diagram information extracted in the step (b) with diagram information of a registered document that is registered in advance, specifying a diagram that is similar in the designated document and the registered document, estimating lines that are similar between the designated document and the registered document; and taking a count of the estimated lines as an estimated a similarity between the data and the registered document; and generating a search result capable of specifying a similar document that is related to the data, based on the estimated similarity; and acquiring data of the registered document from a database in which the registered document is stored, extracting diagram information from the acquired data of the registered document, and updating the contents of a diagram information database storing diagram information of the registered document, using the extracted diagram information. 6. The non-transitory computer-readable recording medium according to claim 5 , wherein, in the step (d), for every registered document, a similarity score indicating a degree of similarity between the registered document and the designated document is computed, based on a line count of the lines estimated in the step (c), as the search result.