An information signal is transmitted. The information signal contains 1) encryption-resultant information, 2) an error correction code signal, and 3) decrypting information. The error correction code signal is designed for correction of at least one error in the encryption-resultant information. The error correction code signal is repetitively completed at a completion period. The decrypting information is designed for decryption of the encryption-resultant information. The decrypting information is repetitively completed piece by piece. At least one compete piece of the decrypting information is dispersively placed in a portion of the information signal which corresponds to the completion period of the error correction code signal.