To easily relate waveform observation results in signals to be measured to S21 characteristics.

A waveform observing apparatus 1 performs interpolation processing of the difference between line spectra of discrete digital waveform data in signals to be measured inputted via a device 70 to be tested and linear spectra for calibration stored in a storage unit 32, and displays waveforms of predicted waveform data obtained by performing inverse Fourier transform of the predicted waveform spectra obtained from spectra of S21 measurement data obtained by smoothing, spectra of S21 adjustment data obtained by varying the frequency of S21 measurement data based on operation from a setting input unit 40 and then by calculation after performing moving averaging again, and spectra for operation obtained by performing Fourier transform to the S21 adjustment data and discrete digital waveform data for calibration stored in the storage unit 32 in parallel in a display unit 60.

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