It is an object to provide an optical transmission module in which an optical transmission line is stably joined to a substrate. An optical transmission module is comprised of an optical element (11) for transmitting or receiving an optical signal, an optical transmission line (10) for optically coupled with the optical element (11), a substrate (12) on which at least one edge portion including entrance and projection portions of the optical signal and the optical element (11) are fixed, wherein a space is defined between the substrate (12) and the transmission line (10), the transmission line (10) can moved in the space in a vertical direction with respect to an optical axis of the optical element (11), and the space is filled with an adhesive(13).