1. A Viterbi detector comprising: (a) means for sequentially receiving a series of symbols representing input amplitude values which tend to be affected by amplitude interference between adjacent symbols; (b) means for generating a plurality of assumed detection values corresponding to the currently-received input amplitude value; (c) means for generating a plurality of Viterbi detection series corresponding to possible survived paths related to the input values; (d) means for generating a plurality of assumed detection value series corresponding to combination of the plurality of the viterbi detection series and the plurality of the assumed detection values; (e) means for generating a data series corresponding to amplitude interference between the adjacent symbols; (f) means for determining assumed input amplitude values in accordance with the assumed detection value series and the data series; (g) means for calculating differences between the assumed input amplitude values and the currently-received input amplitude value; (h) means for calculating likelihoods on the basis of the calculated differences, the likelihoods corresponding to degrees of sureness of the possible survived paths; (i) means for selecting one of the possible survived paths in accordance with the calculated likelihoods; and (j) means for generating a detected value in accordance with the selected survived path.