In a digital-communications system, a receiver presume channel distortion and remove them away from received signals after demodulating. In the latter part, error correction processing is performed and then desired data is obtained. By channel estimation, it is passible to judge that the error rate is large in large channel distortion, and the error rate is small in small channel distortion. Therefore, it is possible to improve the whole error correction capability by presuming the reliability (Confidence) from channel distortion, and utilizing the value as Confidence Factor  in a latter error correction block(FEC). This paper takes Digital Terrestrial Television Broad-casting System as an example, and shows the method that Confidence Factor generated in the receiver block works effectively at the Viterbi decoder on the assumption that it consists of an OFDM demodulation and soft decision Viterbi decoder. The simulation result using MATLAB Simulink and the demonstration system designed on FPGA are described as performance evaluation.