An optical transmission module and method are capable of suppressing the occurrence of multiplexed reflection light, thereby making it possible to easily carry out an optical coupling operation at low cost. A loss generator having an attenuation factor determined based on an extinction ratio of a modulation signal is provided to attenuate reflection light in a transmission path, thereby making it possible to provide a low-cost optical transmission module, which ensures a practically satisfactory efficiency, without providing an optical isolator component. Also, in the optical transmission module, the intensity of light is adjusted by the loss generator. Thus, it is possible to realize the optical transmission module using an optical mounting technique with such accuracy as employed for an ordinary module.