In a measurement by means of OCT, when dispersion is present in a measured target or an optical system in the vicinity of the measured target, resolution of the measurement is degraded. One spectral interference fringe intensity is acquired when a phase difference between measurement light and reference light is not introduced, two spectral interference fringe intensities are acquired in a time-series manner when a phase difference of π is introduced, a required calculation is performed based on the intensity, and a tomographic image not having reduced resolution due to dispersion is acquired.
