An optical measurement device (1) comprising: a hollow cylindrical member (2) having a first opening (10) in one plane and having a second opening (18) in another plane; a rotary mechanism (52, 54) for rotating the cylindrical member along a first axis that is the central axis of the cylindrical member; a support (20, 22) for positioning a light source (30) in a measurement position, on the first axis, that is a position whereby irradiated light enters the interior of the cylindrical member through the first opening; a first reflector (12) disposed in the interior of the cylindrical member to reflect the light entering from the light source through the first opening; a second reflector (14) for reflecting light in the interior of the cylindrical member and transmitting the light to the exterior of the cylindrical member along the first axis through the second opening; and at least one third reflector (16) for making the light reflected by the first reflector incident to the second reflector.