A high-speed optical delay generating method by a rotation reflector in optical coherence tomography, capable of providing a sectional picture with a sufficiently long depth-direction (Z direction) scanning distance, and an optical coherence tomography device therefor are provided. The device comprises a low-coherence light source (1), a half mirror (2) for splitting light from the low-coherence light source (1) into two, that is, into object light towards an object (A) to be examined and reference light, a light delay mechanism (3) for delaying the reference light by means of a rotation reflector (12), a fixed mirror (4) for reflecting/returning the reference light from the light delay mechanism (3), the half-mirror (2) for combining the object light returning from the object (A) to be examined with the reference light returning from the light delay mechanism, and a light detector (11) for detecting interference light including a heterodyne interference beat signal combined at the half mirror (2).