The optical transmission module 1 includes an optical element 10, a first main surface 20SA, and a second main surface 20SB, and a wiring board 20 on which the optical element 10 is mounted on the second main surface 20SB side； The holding member 40 fixed to the first main surface 20SA side of the wiring board 20 and the optical fiber 50 inserted into the through hole H40 of the holding member 40, and the wiring board 20 includes the upper insulating layer 21 and the lower insulating layer 22 include a flat wiring pattern 31 between the wiring layers 30 sandwiched between them, and there is an opening H30 in which the upper surface 31SA and the lower surface 31SB of the wiring pattern 31 are exposed. The end face 50SA of the optical fiber 50 is in contact, and the external electrode 12 of the optical element 10 is joined to the lower face 31SB.光伝送モジュール１は、光素子１０と、第１の主面２０ＳＡと第２の主面２０ＳＢとを有し、第２の主面２０ＳＢ側に光素子１０が実装されている配線板２０と、配線板２０の第１の主面２０ＳＡ側に固定されている保持部材４０と、保持部材４０の貫通孔Ｈ４０に挿入されている光ファイバ５０と、を有し、配線板２０が、上絶縁層２１と下絶縁層２２とにより、挟まれている配線層３０に平板状の配線パターン３１を含み、さらに、配線パターン３１の上面３１ＳＡおよび下面３１ＳＢが露出している開口Ｈ３０があり、上面３１ＳＡに光ファイバ５０の端面５０ＳＡが当接しており、下面３１ＳＢに光素子１０の外部電極１２が接合されている。
