In an optical circuit mounting structure of the present invention, a surface for mounting an optical circuit is implemented as three separate structural members (1, 2, 3) in the form of aluminum plates. The structural member (1, 2, 3) are connected together by hinges (7, 8). Optical parts (4), splices (5), connectors (6) for external lines and so forth are mounted on the circuit mounting surfaces of the structural members (1, 2, 3). The optical parts (4) are interconnected by optical fibers (9). The fibers (9) and their extra length portions (10) are affixed to the structural members (1, 2, 3) by fiber retainers 11. At the portions where the structural members (1, 2, 3) join each other, the fibers (9) intersect the axes of the hinges (7, 8) at an acute angle. After assemblage and adjustment, the structural members (1, 2, 3) are selectively folded upward and downward by 180 degrees about the associated flanges (7, 8) and then affixed together.