1. A document retrieving apparatus, comprising: a processor, wherein the processor is configured to operate in accordance with executable instructions that, when executed, cause the processor to operate as: an extractor receiving a search query for a target document and searching a database by using a threshold of similarity to the target document to extract a plurality of documents having larger similarity than the threshold, the similarity between the target document and the respective extracted documents being a first similarity; a two-dimensional map creator, by using the extracted documents, computing similarity between the respective extracted documents, the similarity between the respective extracted documents being a second similarity, creating a single radar chart in accordance with the first similarity and the second similarity by plotting each of the documents on the single radar chart according to a degree of relevance based on a distance such that the lower the similarity, the further each document is apart from other document, and displaying the created radar chart; an area designator which designates an area on the displayed single radar chart, the area covering at least two plots of a plurality of plots, each associated with the respective documents, in accordance with an input instruction; an area information detector which detects area information representing the designated area for a retrieval with a narrowed range on the displayed map; a document detector which detects documents corresponding to the at least two plots covered by the designated area; a document list reader which reads out a document list which is a list of the detected documents; an in-area information compiler which compiles bibliographic information of each document included in the document list read by the document list reader; and a search engine which performs refine search by using a second query which is a compiling result compiled through the in-area information compiler.