1. A searching method comprising: an extraction step of extracting extracted documents, each of which contains a desired search string, from a plurality of document groups each including a plurality of documents; a preference determination step of determining an output preference for each of the extracted documents in accordance with a predetermined rule; a group determination step of determining, in sequence for each of the plurality of document groups, whether or not the document group is a determined group which contains one or more satisfying documents among extracted documents satisfying a predetermined output condition; and, an output step of outputting, in sequence for each of the plurality of the determined groups, a predetermined number of the satisfying documents contained in the determined group.