A digital signal detection circuit includes a threshold value calculator calculating a threshold value from assumptive sampled values corresponding to various data patterns of a regenerated signal. The regenerated signal is obtained by regenerating data recorded on a recording medium by a regenerating head. The detection circuit also includes a Viterbi decoder carrying out Viterbi decoding of the regenerated signal with the threshold value determined by the threshold value calculator as a constant. The threshold value calculator variably controls the threshold value using a decoded output of the Viterbi decoder and a regenerated signal corresponding to the decoded output of the Viterbi decoder.
