a substrate formed with

an emission-side opening that allows an optical signal to transmit from a first-surface side of the substrate to a second-surface side of the substrate,

a receiving-side opening that allows the optical signal to transmit from the second-surface side of the substrate to the first-surface side of the substrate, and

an inspection opening that is disposed between the emission-side opening and the receiving-side opening;

a light emitting element that is mounted on the first-surface side of the substrate and is disposed in a position where the light emitting element faces the emission-side opening, wherein the light emitting element emits the optical signal;

a light receiving element that is mounted on the first-surface side of the substrate and is disposed in a position where the light receiving element faces the receiving-side opening, wherein the light receiving element receives the optical signal;

an optical waveguide that includes a core and a clad formed around the core, the optical waveguide being formed on the second-surface side of the substrate, the optical waveguide having

a first optical path conversion surface that redirects an optical path of the optical signal transmitting from the emission-side opening into the core,

a second optical path conversion surface that redirects an optical path of the optical signal from the core to the receiving-side opening, and

a portion being exposed to the inspection opening of the substrate and being curved toward the inspection opening; and

a core exposure surface that is formed in the curved portion of the optical waveguide so that the core is exposed out of the clad.