In the present invention, when a request query is different in expression from a viewpoint of a target content description, using a term exchange description in which a term contained in the content description and another term indicating in different expression the term are associated with each other and described, the request query or the viewpoint of the target content description is exchanged with the same term as the viewpoint or request respectively to perform content retrieval. In this way, without describing a plurality of viewpoints in a content description, it is possible to increase the number of expressions for use in request query, and to suppress the redundancy of content description.