The optical transmission module 1 includes an optical fiber 70, an optical waveguide substrate 10 including a core portion 12 and a cladding portion 11, a first light-emitting element 40 disposed on a first main surface 10 SA of the optical waveguide substrate 10 , And a second light emitting element 50 disposed on the second main surface 10SB. The optical waveguide substrate 10 has a first reflecting surface for optically coupling the core section 12 and the first light emitting element 40 M1 and a second reflecting surface M2 for optically coupling the core portion 12 and the first light emitting element 50. The first reflecting surface M1 and the second reflecting surface M2 are formed on the side surface of the core portion 12 When viewed transparent from the direction, they overlap and intersect.光伝送モジュール1は、光ファイバ70と、コア部12とクラッド部11とを含む光導波路基板10と、光導波路基板10の第1の主面10SAに配設された第1の発光素子40と、第2の主面10SBに配設された第2の発光素子50と、を具備し、光導波路基板10が、コア部12と第1の発光素子40とを光結合する第1の反射面M1と、コア部12と第1の発光素子50とを光結合する第2の反射面M2とを有し、第1の反射面M1と第2の反射面M2とが、コア部12の側面方向から透明視すると重畳し交差している。
