A document management system of managing as inter-document relation information a plurality of keywords collected as a set for each document template type and managing link among said keywords includes the document file entry and update steps of selecting at least one of keywords based on a document template type in the inter-document relation information; linking the selected keyword with the document file; and detecting a document file influenced by the document entry and update by using the link between the selected keyword and the document file and the inter-document relation information.