A digital AV data transmitting unit includes a data significance deciding section for deciding the significance degree of digital AV data, and a transmitting-side plurality-of-authentication-rules storing section storing a plurality of types of authentication rules. Also included are a transmitting-side authentication selecting section for selecting one type of authentication rule from the transmitting-side plurality-of-authentication-rules storing means in accordance with a decision result by the data significance deciding section when receiving an authentication request, and a transmitting-side authenticating section for performing authentication in accordance with the selected authentication rule.