In a terminal which received an electronic document with at leastone digital signature, when a user changes the contents of the received electronic document, a new digital signature is produced by enciphering signature data by using a secret key of the user, the signature data including a hash total of the document of a new version, personal information of the user (signatory), and version management information necessary to restore an electronic document of a former version from the electronic document of the new version. The new digital signature and the new version electronic document version are transmitted together with the received digital signature to a next person on a document circulating route.