A clear image of a measurement target in optical coherence tomography (OCT) is obtained while suppressing influence of reflected light from a specific portion. Included are a laser beam source, a beam splitter that splits a laser beam into a signal beam and reference beam; an objective lens that focuses the signal beam onto a measurement target in a container, a unit that moves the signal beam focus position, an objective lens that focuses the reference beam, a reflecting mirror, a flat plate arranged between the objective lens and reflecting mirror, and interference optics that combine the signal beam reflected by the measurement target with the reference beam reflected by the reflecting mirror and having passed through the objective lens. Three or more interference beams with different phases, and photodetectors that detect the interference beams are generated, and two of the objective lenses are the same lenses.