A data transmission method and apparatus for transmitting data such as encrypted content data, wherein a device that is to be a destination of transmission is authenticated and, if the device has not been authenticated, encrypted data read out from a storage unit is decrypted to give decoded data, which then is re-encrypted, based on innate key data acquired from the device that is to be the destination of transmission, to give re-encrypted data. The re-encrypted data is then transmitted to the device that is to be a destination of transmission.