The present invention relates to a phase error estimator, a coherent receiver and a phase error estimating method. The phase error estimator estimates a phase error in an inputted base band electric signal and feeds back said phase error; said phase error estimator comprises: a pre-decider, for judging a phase of data in said base band electric signal in accordance with said feedback phase error; a phase error complex value extracting section, for extracting a real part and an imaginary part of the phase error in accordance with the judgment result of said pre-decider; a phase error determining section, for determining said phase error in accordance with the real part and the imaginary part of the phase error extracted by the phase error complex value extracting section; and a time delay feeding back section, for delaying said phase error by N number of symbols and feeding back the delayed phase error to said pre-decider, wherein N is an integer greater than 1.