1. A document management system that acquires and analyzes acquired digital information for relevance to a matter, the document management system comprising: a screen display unit that displays a document group having a plurality of pieces of document data extracted from the digital information to be determined for relevance to the matter by a user and classification buttons allowing the user to select classification conditions for classifying the document group under predetermined conditions; a processor, and a memory, wherein the memory has stored thereon instructions that, when executed by the processor, causes the processor to: receive information relating to a classification button selected by the user among the classification buttons displayed by the screen display unit as selection information; analyze the document group based on the selection information; classify document data in the document group using the analysis result; instruct the screen display unit to display the document group based on the classification result; for each document group containing the classified document data, receive a result of relevance determination by the user; based on the result of relevance determination, sort the document data included in the each document group for which the relevance determination has been made by the user; select an element commonly appearing in the classified document data; record the selected element; search for the recorded element in the document data; and calculate a score indicating a degree of relevance between the relevance determination result and the document data using the search result and the analysis result, based on an appearance frequency and an evaluation value of the selected element, wherein the evaluation value is learned progressively through numerous iterations of learnings; wherein the processor further: registers a plurality of identification codes as set information, wherein the screen display unit displays the registered set information, and upon the set information being selected by the user, simultaneously assigns at least one of the plurality of identification codes to a document data corresponding to the selected set information.