The present invention relates to an optical transmission module and electronic device, which can realize reduction of stray light at a low cost while maintaining the flexibility of the entire of an optical waveguide. An optical path (4) having a support board (9) comprises a core part (11) and a clad part (12) surrounding the core part (11). A resin part (13A) formed of a resin having a refractive index higher than that of the air outside the optical path is provided in a part of the surface area of the clad part (12) along the optical transmission direction to which optical signals are transmitted. The resin part (13A) has an inclined surface namely a bottom surface (13A1) in which the surface on the opposite side of the clad part (12) is tilted relative to the optical transmission direction. The bottom surface (13A1) forms an acute angle with the surface of the clad part (12) at the opposite side of a light-receiving element (8) in the resin part (13A).