Light emitted from the light source unit divided into measuring light and reference light. An optical path length of the measuring light or the reference light is adjusted and a probe guides the measuring light to an object. The reflected light from the object when the measuring light is projected onto the object and the reference light are multiplexed. Interference light of the reflected light and the reference light which have been multiplexed is detected, and a tomographic image of the object is obtained on the basis of the interference light. The probe is provided with a distance measuring circuit for measuring the distance from the probe to the object, and the optical path length of the measuring light or the reference light is adjusted by the use of the distance to the object measured by the distance measuring circuit to adjust the tomographic image obtainment initiating position.