Abstract: A signal processing device includes an upper amplitude value estimating portion estimating an upper amplitude value based on a peak value of the detection signal and a predetermined median value of a preset range, a lower amplitude value estimating portion estimating a lower amplitude value based on the median value and a bottom value of the detection signal, an offset adjustment signal generating portion generating an offset adjustment signal for offset-adjusting the detection signal in a case where either one of the upper amplitude value or the lower amplitude value is set as a reference value and the other one of the upper and lower amplitude values becomes greater than a set value, an offset adjustment portion offset-adjusting the detection signal based on the offset adjustment signal, and a binarization portion binarizing an output signal from the offset adjustment portion based on a threshold value estimated from the detection signal.