An apparatus enabling abnormality detection of a sample. A first interference optical system scans the sample with first signal light from a first sample optical path, making the first signal light interfere with first reference light from a first reference optical path, to detect first interference light. Optical path length difference between the first sample optical path and first reference optical path is changed based on the detection. A change in the optical path length difference is determined. A second interference optical system scans the sample with second signal light from a second sample optical path, making the second signal light interfere with second reference light from a second reference optical path to detect second interference light. Tomographic information of the sample based on detection of the second interference light is determined. A refractive index profile of the sample is obtained based on the change amount information and tomographic information.
