To determine the place of similar or the same paragraph in different documents to make retrievable the paragraph by converting a known paragraph into plural 1st marker continuous codes, converting the document of a data base into plural 2nd marker continuous codes and evaluating the 1st marker continuous codes with respect to the 2nd marker continuous codes for specifying candidate documents.

The coded known paragraph is received (S46), and a generated maker continuation is stored in a processor (S48). One or two or more paragraphs coded from the document of the data base are received (S50) and stored in the processor (S52). As a retrieval reference for investigating the paragraph of the document in the data base, retrieval is performed while using the marker continuation of the known paragraph (S54). For further investigation, the candidate documents are selected from the data base (S56). Then, continuous column retrieval is performed by continuously and repeatedly comparing the marker continuation of the known paragraph with the marker continuation of the document (S58).