An auto-index method enabling to select words used for heading of an index based on an indexing object extraction condition set by a user. In order to generate an index intended for electronic document files, words and phrases are extracted from document files that may become an object for creating an index, the positions of words and phrases on an electronic publication at the time of extracting are extracted, an indexing object extraction condition inputted by a user is received and extracted words and phrases and the indexing object extraction condition are compared with each other to thereby extract index objective words and phrases.