An optical waveguide includes a lower clad having an upper flat surface and a lower flat surface, a core positioned on the upper flat surface of the lower clad and includes a linear-shaped configuration and two end portions in the longitudinal direction of the linear-shaped configuration, and an upper clad positioned on the upper flat surface of the lower clad in the state of covering the upper flat surface and the core. Further, the core includes the convex configurations protruding in the planer direction from the linear-shaped configuration. The upper clad includes the opening for exposing the convex configurations in a plan view.