To obtain a communication unit that can continuously conduct data communication at a fastest transmission an rate in response to an S/N at all times without the need for re-training even in the case that the S/N is deteriorated due to any cause.

This communication unit is provided with both a consecutive convolution coder that transmits a turbo code and a decoder that decodes the turbo code received via a telephone line by means of the maximum likelihood decoding method by interconnecting convolution coders that outputs a trellis code being a compounding convolution code to identify an information bit and a redundant bit in parallel via an interleaver. The communication unit is provided with a puncturing processing section 1 that selectively transmit a turbo code outputted from the interconnected convolution coders, a trellis code outputted form the interconnected convolution coders and data consisting of only the information bit.