Provided is a light waveguide structure, comprising a base waveguide which includes a taper part in which the width narrows contiguously from one end side toward another end side and a narrow-width part which is joined to the other end side of the taper part and extends from the other end side thereof. Three or more layers of upper part waveguides are layered upon the taper part. These upper part waveguides are configured such that planar shapes in two layers which are adjacent in the layering direction become progressively smaller from the taper parts such that the upper layer does not protrude beyond the lower layer and the thickness of the upper part waveguides progressively increases in the layering direction. A plan view approximate wedge part is provided in which the width becomes contiguously narrower toward the other end side in at least the other end side of each upper part waveguide, and the base waveguide and the end face of the one end side of each upper part waveguide are flush.