Abstract: A transmission section is responsive to first through K-th data signals to transmit a transmission signal through a transmission path to a reception section. The transmission signal has first through K-th frames which carry said first through said K-th data signals and first through K-th transmission unique words, respectively, where K represents a positive integer which is greater than one. The transmission section comprises a first producing section for producing the first through the K-th transmission unique words in accordance with a predetermined unique word and each of first through K-th specific patterns and a second producing section for producing the transmission signal in accordance with the first through the K-th transmission unique words and the first through the K-th data signals. The first through the K-th transmission unique words are different from one another.