An optical transmission line holding member includes a main body that mechanically positions and holds an optical transmission line, and an electrical interconnection used to mount an optical element. The main body includes a holding hole which opens in one surface of the main body and is used to mechanically position and hold the optical transmission line, an guide hole which opens in another surface of the main body, has a diameter larger than that of the holding hole and is coaxially aligned with the holding hole, and a resin storage groove provided in the guide hole. The electrical interconnection is formed on the surface in which the holding hole opens.