The present invention provides an optical transmission module and an assembling method thereof, an electronic device, and an optical transmission method. Even if a board-to-board distance is lower than a bending resistance limit of an optical transmission path (4) (bending resistance cannot be maintained), the optical transmission path (4) is accommodated within the distance to realize a reduced accommodation space. The optical transmission module (1) includes the optical transmission path (4) that performs optical transmission between a first circuit board (20) and a second circuit board (30), and the first circuit board (20) and the second circuit board (30) are disposed opposite to each other. The optical transmission path (4) includes a bending portion (4C) having a folded structure having a bending radius R, and a circumferential portion drawn by the bending radius R is provided substantially perpendicular to board surfaces of the first circuit board (20) and the second circuit board (30).