10. The document clustering system according to claim 2 , wherein the clustering unit, based on the similarity between two documents, performs clustering by a coagulation method or K-MEANS method.
2. A document clustering system comprising: a control device comprising a computer device that executes each of: a concept tree structure acquisition unit that acquires a concept tree structure that represents the hierarchical relationship of a concept of a plurality of words; a document set acquisition unit that acquires a document set, which is a collection of documents; a concept similarity computation unit that finds the concept similarity between two arbitrary words of the document set that was acquired by the document set acquisition unit, the concept similarity being an index indicating the closeness of the two words in a concept; an inter-document similarity computation unit that finds inter-document similarity, which is the degree of semantic similarity between two documents that are included in the document set that was acquired by the document set acquisition unit, based on the concept similarity found by the concept similarity computation unit; and a clustering unit that performs document clustering of the document set based on the inter-document similarity that was found by the inter-document similarity computation unit, wherein the concept similarity computation unit finds the concept similarity for two arbitrary words of the document set that was acquired by the document set acquisition unit such that the concept similarity is a maximum when the frequency of appearance in the document set of higher-order words or words of a subordinate category of the higher-order words that are common to the two words in the concept tree structure that was acquired by the concept tree structure acquisition unit coincides with the frequency of appearance in the document set of each of the two words, and is a minimum when there are no common higher-order words of the two words in the concept tree structure.