To easily and correctly measure a sample such as nails, pulled teeth, etc., by an OCT.

A layered fine structure of a sample S is measured by an apparatus according to interferometric method using a low interference light, whereby a low coherent light is brought into the sample S and a reference mirror, and an interference signal between the light reflected or scattered from the sample S and the light reflected from the reference mirror is measured. The apparatus is provided with a sample stage 1 a set face of which for the sample S is rotatably arranged to a horizontal plane, a probe 1 for sending the low coherent light to the sample S, and a probe position adjustment means 20 for adjusting a position in an X axis, a Y axis or a Z axis direction of the probe 1.