5. The searching method according to claim 4 , wherein, the preference determination step determines a lower output preference to the extracted document not containing the search string in the headword than the extracted document containing the search string in the headword.
6. The searching method according to claim 5 , wherein, the extraction step extracts, as the extracted document, the document containing the search string in the headword, and when a number of extracted documents does not reach a predetermined maximum number, further extracts the document containing the search string in the explanatory text.