To accurately measure even signal light varied in polarization and to also measure even the data of polarization.

This optical sampling waveform measuring instrument is constituted so as to convert the light signal, obtained by sampling signal light to be measured by sampling light of which the pulse width narrower than that of the signal light to be measured, to an electric signal by a photoelectric conversion means through a non-linear optical crystal to display a measuring result and is equipped with a means wherein the signal light to be measured and the sampling light are separated into first polarizing component light and second polarizing component light of which the polarizing direction crossing the first polarizing component light at a right angle, and the first polarizing component light of the signal light to be measured and the second polarizing component light of the sampling light are combined while the second polarizing component light of the signal light to be measured and the first polarizing component light of the sampling light are combined and a display means for displaying the waveform of the signal light to be measured on the basis of electric output obtained from the output of the means through two sets of the non-linear optical crystal and the photoelectric conversion means.