This invention relates to an optical coherence tomography, in which a light source and an optical linear beam forming system are adopted to obtain two dimensional image of high quality resolution within short time without affection by any mechanical movements. For such purpose, the optical linear beam forming system (20) comprises semicy Under lens (21), convex lens (22) and slit (23) to implement the frequency domain optical coherence tomography. Parallel light beam from the light source is incident on the surface of the semicylinder lens (21), and focal line of the semicylinder lens (21) is located in front of the convex lens (22). The convex lens (22) has short focal point where the parallel light component converges and long focal point where the diverging light component converges. The slit (23) is located between the short focal point and the long focal point.