A streaming system includes an authoring unit (2), a stream server (3) and a client terminal (5). The authoring unit generates a file composed of encrypted contents data and the ancillary information at least containing the packetizing control information for generating an RTP packet, a non-encrypted codec dependent header made up of the information pertinent to encoded contents data, and the encryption information for decrypting the encrypted contents data form packet to packet. The streaming server packetizes the encrypted contents data along with at least the codec dependent header and distributes the resulting data as a stream. The client terminal refers to the codec dependent header of the received packet, re-assembles the packet, and decrypts the encrypted contents data of the re-assembled packet to generate contents data.