The optical signal to noise ratio is improved when the polarization multilevel signal light 151 is demodulated. A optical polarization multilevel signal receiving apparatus is provided with a polarization multilevel receiver 150 configured to generate at least one estimation symbol A1 to AN estimating a state of the symbol A by utilizing a polarization state of at least one polarization multilevel symbol received in a past before the symbol A, a past value of a decision variable, and a decision result, average the estimation symbols A1 to AN and the symbol A to calculate a reference symbol Ar, and use the calculated reference symbol Ar in place of the symbol A to calculate a decision variable corresponding to a polarization state change of the received symbol R, where R is a received symbol and A is at least one past symbol used as a reference for a change.
Polarization multilevel signal optical receiving apparatus, polarization multilevel signal optical transmitting apparatus, and polarization multilevel signal optical transmission apparatus