A document classification system is provided. The document classification system analyzes digital document information which is collected to be submitted as evidence in a lawsuit and classifies the digital document information. The document classification system includes an extraction unit that extracts documents from the collected document information, a document display unit that displays an extracted document group, a classification code receiving unit that receives a classification code assigned to the displayed document group, a selection unit that classifies the extracted document group for each classification code, analyzes a keyword commonly appearing in the classified document group, and selects the keyword, a database that records the selected keyword, a search unit that searches for the keyword from the document information, a score calculation unit that calculates a score indicating connection between the classification code and the document, and an automatic classification unit that automatically assigns the classification code.