An optical transmission module includes: a package; a plurality of light-emitting elements each emitting light in the interior of the package; a beam splitter splitting the light into transmitted light and split light; a plurality of light-receiving elements each including a light-receiving surface on which the split light is incident in the interior of the package, for monitoring light outputs of the plurality of light-emitting elements; and a first light-shielding film provided between the plurality of light-emitting elements and the beam splitter and including a plurality of first holes for the light to propagate to the beam splitter, wherein the plurality of light-receiving elements are disposed with the light-receiving surfaces facing the beam splitter.