An optical transmission/reception device (1, 1a, 1b) for transmitting or receiving an optical signal via a communication path in which a phase change of the optical signal is suppressed, the optical transmission/reception device comprising: a transmission device comprising: a framer generation unit for mapping an information signal to a data frame for optical transmission; a symbol mapping unit for multi-level modulating the information signal of the data frame; and an optical modulation unit for converting the data frame multi-level modulated by the symbol mapping unit into an optical polarization multiplexed signal by superimposing the data frame on a plurality of polarizations of an optical carrier wave, and transmitting the optical polarization multiplexed signal to the communication path; and a reception device comprising: an optical reception front end unit for receiving an optical polarization multiplexed signal from a communication opponent via the communication path, and converting an optical signal that is obtained by causing interference between the received optical polarization multiplexed signal and a continuous wave local oscillation light oscillated by a local oscillator, into analog electric signals; an A/D conversion unit for converting the analog signals into digital signals; a polarization separation unit for separating the received optical polarization multiplexed signal into a plurality of polarization signals using the digital signals; a phase estimating unit for estimating a first phase of a first polarization being a phase of at least one of a plurality of polarizations from the plurality of polarization signals separated by the polarization separation unit; and a framer terminating unit for demapping an information signal from a data frame; characterized in that the phase estimating unit is configured for estimating the first phase or a phase obtained by correcting the first phase, as a second phase of a second polarization being different from the first polarization, wherein the phase estimating unit is configured to estimate a phase shift between the first polarization and the second polarization, and to estimate the second phase on a basis of the estimated phase shift and the first phase, and wherein the data frame includes the first and second phases estimated by the phase estimating unit. a transmission device comprising: a framer generation unit for mapping an information signal to a data frame for optical transmission; a symbol mapping unit for multi-level modulating the information signal of the data frame; and an optical modulation unit for converting the data frame multi-level modulated by the symbol mapping unit into an optical polarization multiplexed signal by superimposing the data frame on a plurality of polarizations of an optical carrier wave, and transmitting the optical polarization multiplexed signal to the communication path; and a reception device comprising: an optical reception front end unit for receiving an optical polarization multiplexed signal from a communication opponent via the communication path, and converting an optical signal that is obtained by causing interference between the received optical polarization multiplexed signal and a continuous wave local oscillation light oscillated by a local oscillator, into analog electric signals; an A/D conversion unit for converting the analog signals into digital signals; a polarization separation unit for separating the received optical polarization multiplexed signal into a plurality of polarization signals using the digital signals; a phase estimating unit for estimating a first phase of a first polarization being a phase of at least one of a plurality of polarizations from the plurality of polarization signals separated by the polarization separation unit; and a framer terminating unit for demapping an information signal from a data frame; characterized in that the phase estimating unit is configured for estimating the first phase or a phase obtained by correcting the first phase, as a second phase of a second polarization being different from the first polarization, wherein the phase estimating unit is configured to estimate a phase shift between the first polarization and the second polarization, and to estimate the second phase on a basis of the estimated phase shift and the first phase, and wherein the data frame includes the first and second phases estimated by the phase estimating unit.