Abstract: An optical branch module including a glass block, an input/output gradient index lens, an output gradient index lens, a beam splitter film, a mirror film, an input optical fiber, a first output optical fiber that extracts input light from the input optical fiber reflected by the beam splitter film as first output light, and a second output optical fiber that extracts light passed through the beam splitter film passed through the glass block, reflected by the mirror film, passed through the glass block again, and input from the other end of the output gradient index lens as second output light.