An optical waveguide includes a substrate, an upper clad layer arranged on the substrate; and an optical waveguide structure that is disposed in the upper clad layer so as to be parallel to a surface of the substrate. The optical waveguide structure includes a flat optical waveguide, channel optical waveguides that are each connected with a first edge face of the flat optical waveguide and extend radially therefrom, the channel optical waveguides each respectively have lateral sides parallel to the substrate surface that have a width therebetween which increases as the distance from the first edge face increases, and an input optical waveguide connected with a second edge face that is arranged at an side of the flat optical waveguide opposite to the first edge face.