A client unit 1 which a user uses to request for data, an agent unit 2 which keeps encrypted document data and attributes information, a document managing unit 3 which executes user authentication, access control and document image edition by means of decrypting of encrypted document data each have a processing function and an interface function which are independent of each other, and are connected via a communication network. This realizes a new data managing method which makes it easy to retrieve document data from a database through an on-line use or to search, output and otherwise document data in a single computer system, and therefore, a high level of security is achieved.