To lessen interference noise in an optical coherence tomography device (OCT)-purpose optical interference unit.SOLUTION: An optical interference unit of an OCT 100 has: an interferometer; and a detection module 114. The interferometer has: a first coupler 103 that divides an optical beam into specimen-purpose measurement light and reference light; a second coupler 112 that is configured so that both the reference light exiting the first coupler and the reflection light from the specimen interfere with each other with both light incident upon the second coupler; first connection fiber transmission bodies 105, 116 and 113 that connect either end of these couplers; a second connection fiber transmission body 111 that connects other ends themselves of the two couplers; an optical element 117 that is in the middle of the first connection fiber transmission body; a first fiber route 118 that extends between the optical element and the second coupler; and a second fiber route 119 that extends between the optical element and the second coupler, and has a length with a predetermined relationship with respect to a length of the first fiber route.SELECTED DRAWING: Figure 1
OPTICAL COHERENCE TOMOGRAPHY DEVICE-PURPOSE OPTICAL INTERFERENCE UNIT