The document retrieval unit retrieves documents in a set of retrieval object documents stored in the memory unit according to the entered retrieval condition such as retrieval word, sequences each document depending on the goodness of fit to the retrieval condition, and issues the retrieval result by shuffling the documents in the sequence by occurrence. The occurrence distribution calculating unit calculates the occurrence distribution of retrieval conditions from this sequenced retrieval results and the table of sets of sample documents stored in the memory unit. The retrieval history storage unit stores the entered retrieval condition, the sequenced retrieval result from the document retrieval unit, and the occurrence distribution of retrieval conditions calculated by the occurrence distribution calculating unit in the memory unit as retrieval history. The retrieval history processing unit graphically processes the retrieval history stored in this memory unit, and calculates the occurrence distribution of retrieval condition in each set of sample document, so that the user can easily judge the validity of the retrieval condition and the effect of the retrieval condition on the retrieval result.