Abstract: A signal detection device and method of a data recording/reproducing apparatus. The signal detection device of a data recording/reproducing apparatus for recording/reproducing a digital signal U.sub.k having an arbitrary integer time k as an index, includes: an analog-to-digital converter (ADC) for converting an analog signal from which external band noise is removed after being reproduced from the data recording/reproducing apparatus, into a digital signal; a filter for modifying the digital signal converted by the analog-to-digital converter (ADC) into a signal having a predetermined spectral shape; and a Viterbi detector for detecting the spectrum signal modified by the filter as the data recorded in the data recording/reproducing apparatus. Therefore, after equalizing a signal into a spectrum expressed by 2+D+D.sup.2 +D.sup.3, which is similar to the spectrum of an optical recording/reproducing apparatus, the maximum likelihood (ML) is detected by the Viterbi detector.