1. A document classification system comprising a processing apparatus comprising: a document extraction circuitry which extracts a predetermined number of documents as a subject to be classified by a user by sampling the predetermined number of documents from document information; a display circuitry which displays a document display screen presenting the user with the extracted documents and one or more classification marks for classifying the documents, enabling the user to select the one or more classification marks to classify the extracted documents; a classification mark accepting circuitry which accepts the one or more classification marks attached to each of the displayed document and selected by the user; a database which records words which appear in common in the documents to which a given classification mark is attached; and a score calculation circuitry which, for each of the documents from the document information, calculates a score which is the evaluation of the relation between the document and the classification mark based on the amount of information which is exhibited by the recorded words in the document.