PROBLEM TO BE SOLVED: To provide a technology for reducing an estimation error of a beat noise estimator by reducing influence by the fluctuation of a bit pattern.SOLUTION: A beat noise estimator 13 includes: a delay element 21 giving a time delay to a reception electric signal 91 output by a photoelectric converter 11; a subtractor 22 subtracting a signal component estimation value 92 output by a maximum likelihood determination unit 12 from the reception electric signal 91 whose time is delayed by the delay element 21, and outputting a noise signal 95 obtained by removing a signal component from the reception electric signal 91; and a correlator 23 outputting, as a beat noise estimation value 93 after correction, a value obtained by correcting a beat noise estimation value before correction, which is calculated from a correlation between the noise signal 95 output by the subtractor 22 and the signal component estimation value 92 output by the maximum likelihood determination unit 12, by a pseudo beat noise estimation value calculated from a multiplication value of the signal component estimation value 92 on the plurality of signal components targeted for beat noise estimation output by the maximum likelihood determination unit 12.