A light physical constant measurement method for measuring distribution of light physical constants within an optical transmission medium, the light physical constant measurement method comprising: obtaining information indicating a power spectrum and a phase spectrum of an input optical signal of a plurality of intensities; measuring, for each of the plurality of intensities of the input optical signal, a power spectrum of an output optical signal that is output after the input optical signal of the intensity propagates within the optical transmission medium; virtually dividing the optical transmission medium along a propagation direction to set a plurality of first segments; estimating (S108, S110, S112, S114) light physical constants of the plurality of first segments based on a result of a first propagation simulation that uses a model in which the input optical signal of each of the plurality of intensities propagates sequentially through the plurality of first segments; and outputting the estimated light physical constants of the plurality of first segments as the distribution of the light physical constants within the optical transmission medium, wherein the first propagation simulation requires, as input, the obtained information indicating the power spectrum and the phase spectrum of the input optical signal of the plurality of intensities, and light physical constants of the plurality of first segments, and outputs a power spectrum of the output optical signal as a simulation result, in the estimating of light physical constants of the plurality of first segments, the light physical constants of the plurality of first segments are searched for using an evaluation function of evaluating a difference between the measured power spectrum of the output optical signal and the power spectrum of the output optical signal obtained as a result of the first propagation simulation, to estimate the light physical constants of the plurality of first segments, and the light physical constants include a nonlinear optical constant and a dispersion parameter. obtaining information indicating a power spectrum and a phase spectrum of an input optical signal of a plurality of intensities; measuring, for each of the plurality of intensities of the input optical signal, a power spectrum of an output optical signal that is output after the input optical signal of the intensity propagates within the optical transmission medium; virtually dividing the optical transmission medium along a propagation direction to set a plurality of first segments; estimating (S108, S110, S112, S114) light physical constants of the plurality of first segments based on a result of a first propagation simulation that uses a model in which the input optical signal of each of the plurality of intensities propagates sequentially through the plurality of first segments; and outputting the estimated light physical constants of the plurality of first segments as the distribution of the light physical constants within the optical transmission medium, wherein the first propagation simulation requires, as input, the obtained information indicating the power spectrum and the phase spectrum of the input optical signal of the plurality of intensities, and light physical constants of the plurality of first segments, and outputs a power spectrum of the output optical signal as a simulation result, in the estimating of light physical constants of the plurality of first segments, the light physical constants of the plurality of first segments are searched for using an evaluation function of evaluating a difference between the measured power spectrum of the output optical signal and the power spectrum of the output optical signal obtained as a result of the first propagation simulation, to estimate the light physical constants of the plurality of first segments, and the light physical constants include a nonlinear optical constant and a dispersion parameter.