An optical transmission module includes a light emitting device for transmitting a first optical signal, a light receiving device for receiving a second optical signal, an optical fiber for guiding a third optical signal in which the first optical signal and the second optical signal are coupled, and an optical waveguide substrate having an optical waveguide made of first resin, wherein a groove formed on the optical waveguide substrate is provided with a prism having the optical fiber and a reflective face through which the first optical signal transmit, a first side face of the prism contacts a first wall face of the groove, and a second side face thereof contacts a second wall face of the groove.
