When reflection light, reflected from a measurement target that has been irradiated with measurement light in such a manner to scan the measurement target, and reference light are combined in each wavelength sweep, interference light is detected as interference signals. When a thinning region in which the interference signals obtained by detecting the interference light in each wavelength sweep are thinned so that the interference signals that are used to produce the tomographic image remain is set, thinning is performed on the plurality of interference signals in the thinning region. Light intensity information about the measurement target in the thinning region is obtained, based on the interference signals for the respective wavelength sweeps, the interference signals remaining after thinning. The tomographic image in the thinning region is produced based on the obtained light intensity information.
