Abstract: In a conventional document classification method, because a document is classified by only adaptability of an occurrence word of a document with a conditional expression of each folder, abstract levels of a classified folder and description contents of the document do not match or it is difficult to discriminate a field and a theme. The present invention obtains a candidate rate of a folder by classification adaptability into the folder and abstract adaptability among folders on one layer. The folder into which the document ought to be classified in accordance with a value of the candidate rate is decided, and then a folder layered structure to which the document ought to be assigned is decided using folder candidate distribution.