An optical tomographic apparatus is provided and includes a light source portion, and an interferometer including a probe. A vicinity of a fore-end of a probe is provided with a concave mirror and a portion spaced apart from the concave mirror by a distance therebetween is provided with a semitransparent mirror and a GRIN lens successively from a fore-end side of the probe. On the other hand, the probe includes light transmitting window portions at positions different from each other by 180 degrees in a peripheral direction thereof, and a subject can be irradiated and subject light can be acquired in two directions in the peripheral direction of the probe. Thereby, there is constructed a constitution capable of acquiring information twice as much as that of a related art by one time irradiation to the subject by a comparatively simple constitution.