In an optical waveguide 10 with a light emitting device to be used in the present invention, branched points 16 are sequentially provided in a guiding light direction 17 of a main path 14 and the width of the main path 14 becomes narrower as the main path 14 moves away from a light emitting device 11. The optical waveguide 10 having this structure can reduce a width W1 because there are no portions that correspond spaces (cladding layers) among adjacent branched paths 15. Moreover, the optical waveguide 10 has an excellent optical transmission efficiency, resulting in high intensity of light emitted. Uniformity of the light emitted is equal or more than a conventional optical waveguide 60 with a light emitting device.