A parallel signal of a k bit width is converted such that every m bits of width is made a byte. It is then coded by a plurality i of encoders into a t byte error correcting code in which a byte length is of m bits and a code length is of 1 bytes. The coded parallel signal is interleaved by an interleaver and is distributed into a plurality 1 of transmitters. Each transmitter converts the parallel signal of an mi bit width into a serial signal and transmits the converted signal. Each receiver converts the received serial signal into a parallel signal of an mi bit width and outputs the signal thus converted. The signals outputted from a plurality i of receivers are deinterleaved by a de-interleaver, and the deinterleaved signals are inputted to a plurality i of decoders. The decoders carry out correction of a t byte error in which one byte is of m bits, and integrates the signals outputted therefrom and outputs a parallel signal of a k bit width. By making use of the byte error correcting code, the interleaver, and the deinterleaver, the parallel data transmission unit provides for the correction of a byte error having a byte length longer than that of the code, and also provides for the reduction in scale of the encoders and decoders. Each of i, k, l, and m is an integer not less than 2.