To output an appropriate retrieval object document or an appropriate retrieval number as a retrieved result by setting an appropriate judgement threshold value corresponding to individual retrieval requests.

This method sets the judgement threshold value in a retrieval processing using a vector space method for scoring the similarity degree of the vector expression of the retrieval request and the vector expression of the retrieval object document retrieved based on the retrieval request and outputting the retrieval object document exceeding a prescribed judgement threshold value as the retrieved result. In this case, an ideal document assumed as the retrieved result by the retrieval request is prepared (S301 and S302) as a model document from the retrieval request inputted as the retrieval condition of the retrieval processing, the similarity degree of the vector expression of the prepared model document and the vector expression of the retrieval request is obtained, the value is set (S303) as an ideal value and the value of the similarity degree separated from the obtained ideal value for a prescribed value is set (S304) as the judgement threshold value.