The present invention can quickly and easily perform processing for clustering a plurality of documents, and for deciding the central document of each cluster. A document clustering device 102 is provided with a document group storing part 118 for storing a document group, a keyword extracting part 18 for extracting a keyword from the document group, a similarity information retrieving part 20 for calculating similarity among all the documents, a similarity table 30 for storing the similarity, a clustering part 22 for clustering the documents based on the bias of the distribution of the similarity, a central document calculating part 112 for calculating the central document of each cluster, and a clustering information preparing part 114 and a clustering information storing part 120 for preparing and storing information related with each cluster. The device 102 is also provided with a document classifying part 116 for comparing an additional document with the characteristic document of each cluster, and for classifying it. |