A transmitting apparatus 100 includes an initialization vector generating unit 110 for generating initialization vector IV1-IV5 for encrypting stream data with a stream encryption method, wherein the initialization vector is changed at every initialization intervals defined by a stream encryption module; an initialization packet generating unit 140 for generating an initialization packet IP containing an initialization vector used when stream data following the initialization packet are encrypted and another initialization vector used when another stream data different from the stream data following the initialization packet are encrypted; an encryption unit 120 for initializing the stream encryption module using a generated initialization vector, and performing stream encryption on stream data following the initialization vector; an encryption packet generating unit 130 for generating an encryption packet EP containing stream-encrypted data; and a transmission unit 150 for transmitting the initialization packet IP and the encryption packet EP by broadcast/multicast.