To realize a wavelength dispersion measuring apparatus capable of measuring wavelength dispersion with high precision.

The wavelength dispersion measuring apparatus, which measures the wavelength dispersion and a group delay time, is equipped with first and second variable wavelength light sources emitting continuous light beams whose oscillation wavelengths can be varied, and being synchronously controlled so that the difference frequency between the emitted light beams is kept constant at any time; a light composing/dividing means composing respective output light beams of the first and second variable wavelength light sources, converting it into an optical signal which has variations in light intensity of the difference frequency, and dividing the light signal into two components; and an optical sampling oscilloscope receiving one divided component of the optical signal which passes through an object to be measured, and displaying waveforms while using the other divided component of the optical signal as a trigger signal. The waveforms are observed at each wavelength of the output light beams of the first and second variable wavelength light sources, while varying the wavelength respectively, and the group delay time is obtained from respective observed waveforms.