PURPOSE: To shorten the retrieval time by leading a concept of an equivocation into each keyword in a retrieval condition and allowing a user to designate and give it.

CONSTITUTION: Between a file accuracy calculating part 19 and a request processing part 15, a keyword association degree converting part 20 is provided, and from a keyboard, a request with an equivocation is inputted. That is, when a retrieval condition by the keyword number and others is inputted as a request from the keyboard, an attribute of a concept of an equivocation having a value of a binary or above is designated and given to each keyword. In such a way, since the concept of an equivocation is led into each keyword in the retrieval condition and a user is allowed to designate and give it, it is useful for the reduction of a result of retrieval, the retrieval time is shortened and the document retrieval of a suitable quantity and a suitable quality is obtained.