An optical waveguide structure includes: a cladding; a first core in the cladding having a first end surface; a second core in the cladding having a second end surface; slit formed horizontally with respect to a waveguide direction of the light to be waveguided by the first and second cores; and a first part and a second part composed of a material identical to a material of the cladding, wherein a pair of the first and second end surfaces disposed opposing each other with the slit interposed between the pair of the first and second end surfaces, the first part is interposed between the first end surface and the slit, and the second part is interposed between the second end surface and the slit.