An optical waveguide includes: a first clad layer; a core layer formed on the first clad layer; a second clad layer formed on the core layer; and an optical transmission direction changing part. The optical transmission direction changing part is configured and arranged to change a transmission direction of a light transmitting through the core layer. The optical transmission direction changing part penetrates through the core layer. An optical transmission direction changing surface of the optical transmission direction changing part inclines relative to a predetermined reference plane by a predetermined angle.