A storage location and a name of a document designated by a user are displayed on a main window screen. A viewing history management section determines if the information in display has been viewed before by referring to a content of a document management information storage section, acquires an ID number corresponding to the information if viewed before, and, if not, issues a new ID and registers it in the storage section. A list of a related document group is created by analyzing viewing history information accumulated daily, determining a document group related to a document in view, and creating the group as a list.