A waveform reconstruction device (140) is provided with the following: a phase spectrum calculation unit (143) for (a) calculating, for the strengths of input optical signals, a computed power spectrum of an output optical signal by performing propagation simulation within the light transmission medium of an input optical signal assuming that the input optical signal has a given phase spectrum, and for (b) retrieving the phase spectrum of the input optical signal by changing the given phase spectrum so that the differences between the computed power spectrum and a measured power spectrum become smaller for the strengths of the input optical signals, and by repeating propagation simulation; and a waveform reconstruction unit (144) for reconstructing the temporal waveform of an input signal using the retrieved phase spectrum. The phase spectrum calculation unit (143), on the basis of either non-linear optical effects or distribution effects, changes the given phase spectrum or performs propagation simulation.