1. A document management system that acquires digital information recorded in a plurality of computers or a server and analyzes the acquired digital information for relevance to a lawsuit, 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 lawsuit by a user and classification buttons allowing the user to select classification conditions for classifying the document group under predetermined conditions; a selection information reception unit that receives information relating to a classification button selected by the user among the classification buttons displayed by the screen display unit as selection information; a classification instruction unit that analyzes the document group based on the selection information, classifies document data in the document group using the analysis result, and instructs the screen display unit to display the document group based on the classification result; a result reception unit that receives a determination result of relevance by the user on the document group classified by the classification instruction unit; a selection unit that classifies document data included in the document group determined for relevance by the user for each determination result based on the determination result and analyzes and selects an element commonly appearing in the classified document data; an element recording unit that records the selected element; a search unit that searches for an element recorded in the element recording unit from the document data; and a score calculation unit that calculates a score indicating relevance between the determination result and the document data using a search result of the search unit and an analysis result of the selection unit.