1. A method of detecting an orientation of an optical fiber that is provided in an optical-transparent maintaining member including a flat surface as a part of a surface of the maintaining member, the method comprising: directing collimated light to the optical fiber through the flat surface of the maintaining member; receiving reflected light of the collimated light by using an optical sensor device; generating a brightness distribution image according to an output signal from the optical sensor device; identifying a reference point on a brightness distribution line appearing on the generated brightness distribution image, according to a position of the brightness distribution line in relation to a target orientation for the optical fiber, the brightness distribution line detectable on the brightness distribution image in correspondence to the reflected light received by the optical sensor device; and detecting the orientation of the optical fiber according to a coordinate of the reference point on the brightness distribution image.