PURPOSE: To improve the operability of a document retrieval using an index.

CONSTITUTION: A document constituted in the unit of a page is accumulated in a document accumulating means 21, document retrieval index data is added to its accumulated document by an index data adding means 22, and an arbitrary document accumulated by the added document retrieval index data is retrieved by a document retrieving means 23. Subsequently, a mark is added to an arbitrary page of a document managed by a document managing means 20, by a mark adding means 25, a page to which the mark is added in the document accumulated by using the mark retrieval index data is retrieved by a mark added page retrieving means 26, and the document retrieval index data and the mark retrieval index data are accumulated by the same data format by an index data accumulating means 27.