A digital coherent receiver comprising: a digital converter arranged to sample a signal received from an optical transmission path and to generate a digital signal; a sampling phase detector arranged to detect a phase of the sampled digital signal; a phase adjustor arranged to adjust a sampling phase of the digital signal based upon the detected phase; and a demodulator arranged to demodulate the phase-adjusted digital signal, wherein the phase detector includes: two or more filters (60-0 to 60-n) arranged to equalize the digital signal with different equalization characteristics; two or more sensitivity monitoring phase detectors (70-0 to 70-n), each connected to one of the filters and configured to output a phase detection signal representing a phase of an output signal from the associated filter and a sensitivity monitoring signal representing a sensitivity of the phase detection, the sensitivity of the phase detection being expressed by the slope of a line relating an amplitude of the outputted phase detection signal to a phase of an input signal to the phase detector, at a linear region in the vicinity of the zero crossing point; two or more sensitivity correction coefficient generators (75-0 to 75-n), each arranged to generate a sensitivity correction coefficient for correcting the associated phase detection signal using a square sum of all the sensitivity monitoring signals; and an adder arranged to add the phase detection signals that have been corrected by the sensitivity correction coefficients and to output a phase signal. a digital converter arranged to sample a signal received from an optical transmission path and to generate a digital signal; a sampling phase detector arranged to detect a phase of the sampled digital signal; a phase adjustor arranged to adjust a sampling phase of the digital signal based upon the detected phase; and a demodulator arranged to demodulate the phase-adjusted digital signal, wherein the phase detector includes: two or more filters (60-0 to 60-n) arranged to equalize the digital signal with different equalization characteristics; two or more sensitivity monitoring phase detectors (70-0 to 70-n), each connected to one of the filters and configured to output a phase detection signal representing a phase of an output signal from the associated filter and a sensitivity monitoring signal representing a sensitivity of the phase detection, the sensitivity of the phase detection being expressed by the slope of a line relating an amplitude of the outputted phase detection signal to a phase of an input signal to the phase detector, at a linear region in the vicinity of the zero crossing point; two or more sensitivity correction coefficient generators (75-0 to 75-n), each arranged to generate a sensitivity correction coefficient for correcting the associated phase detection signal using a square sum of all the sensitivity monitoring signals; and an adder arranged to add the phase detection signals that have been corrected by the sensitivity correction coefficients and to output a phase signal. two or more filters (60-0 to 60-n) arranged to equalize the digital signal with different equalization characteristics; two or more sensitivity monitoring phase detectors (70-0 to 70-n), each connected to one of the filters and configured to output a phase detection signal representing a phase of an output signal from the associated filter and a sensitivity monitoring signal representing a sensitivity of the phase detection, the sensitivity of the phase detection being expressed by the slope of a line relating an amplitude of the outputted phase detection signal to a phase of an input signal to the phase detector, at a linear region in the vicinity of the zero crossing point; two or more sensitivity correction coefficient generators (75-0 to 75-n), each arranged to generate a sensitivity correction coefficient for correcting the associated phase detection signal using a square sum of all the sensitivity monitoring signals; and an adder arranged to add the phase detection signals that have been corrected by the sensitivity correction coefficients and to output a phase signal.