A data transmission method for transmitting data, whose copying is controlled, performed by a data transmission device complying with Digital Transmission Content Protection over IP, DTCP-IP, the data transmission method comprising the steps of: performing an authentication procedure between the data transmitting device and a data receiving device; setting first copy control information, wherein the set first copy control information includes copy control information prescribing whether or not data copying is allowed, and includes information of an encryption mode responding to whether or not the data copying is allowed; setting second copy control information, wherein the set second copy control information includes information concerning output control of the data; generating and transmitting a packet to the data receiving device, the packet including a header including the first copy control information and the second copy control information, and a payload obtained by encrypting the data with a predetermined data key, wherein, under a transmission-system environment in which data transmission is performed by using a packet having a format including a header including a field in which the first copy control information is written and a payload including data in which data-embedded copy control information is embedded, the set second copy control information includes mode information representing validity of the second copy control information included in the header and includes substitution information representing substitutability of the data-embedded copy control information concerning the first copy control information, wherein under the transmission-system environment, the data is encrypted by using a data key generated by using a nonce, and the header includes a field for transmitting a nonce having a predetermined bit length; and in the step of generating and transmitting the packet, the packet is transmitted in a form in which the second copy control information is embedded in the field for transmitting the nonce. performing an authentication procedure between the data transmitting device and a data receiving device; setting first copy control information, wherein the set first copy control information includes copy control information prescribing whether or not data copying is allowed, and includes information of an encryption mode responding to whether or not the data copying is allowed; setting second copy control information, wherein the set second copy control information includes information concerning output control of the data; generating and transmitting a packet to the data receiving device, the packet including a header including the first copy control information and the second copy control information, and a payload obtained by encrypting the data with a predetermined data key, wherein, under a transmission-system environment in which data transmission is performed by using a packet having a format including a header including a field in which the first copy control information is written and a payload including data in which data-embedded copy control information is embedded, the set second copy control information includes mode information representing validity of the second copy control information included in the header and includes substitution information representing substitutability of the data-embedded copy control information concerning the first copy control information, wherein under the transmission-system environment, the data is encrypted by using a data key generated by using a nonce, and the header includes a field for transmitting a nonce having a predetermined bit length; and in the step of generating and transmitting the packet, the packet is transmitted in a form in which the second copy control information is embedded in the field for transmitting the nonce. <EOS>