To reduce a cost burden of security management without installing a server for key management of each user.

An encryption server generates an encryption key of an electronic file, and encrypts the generated encryption key of the electronic file by a master key. The encryption key of the electronic file and the encryption key of the electronic file encrypted by the master key are transmitted to a client terminal, and the client terminal stores the received encryption key of the electronic file and the encryption key of the electronic file encrypted by the master key, encrypts the electronic file by use of the stored encryption key of the electronic file encrypted by the master key, and adds the encryption key of the electronic file encrypted by the master key to the encrypted electronic file to generate an information file.