6. The document information search method according to claim 1, wherein: generating a plurality of presearch files corresponding to a character string length extracted from said text file, and narrowing down an object text by presearching the presearch files for a short character string length extracted from said text file.
1. A document information search method for searching for specified text data containing a given search subject key word from a group of documents including document text data stored in advance, said method comprising the steps of: registering text data of said documents as a source file, generating a presearch file representative of component characters of the document text data in the source file, generating a search query component character file comprising character components of the given search subject key word, selecting as possible search documents for key word searching, selected ones of the documents having a presearch file including the character components of the search query component character file; and key word searching of the selected ones for the given search subject key word.