PURPOSE: To execute a retrieval by a paragraph unit, and to execute an exact and high speed retrieval in accordance with a purpose by providing a means for discriminating the part corresponding to an item stored in a format storage means and retrieving its index.

CONSTITUTION: As for a document inputted by a document input means 1, in an index preparing means 2, paragraph-constituting information of the document classification concerned is obtained by referring to format data in a format storage means 5, and divided into plural paragraphs. These respective paragraphs are collected at every classification, and prepared as an index. The index generated by the index generating means 2 is stored by an index storage means 3. A fixed length paragraph index storage means 19 can manage index data by data of one table format, because data length of the paragraph is determined. In such a way, in the fixed length paragraph index storage means 19, a relational data base can be realized, and a high speed retrieval can be executed.