To introduce an optical waveguide loupback device having low loss and gentle manufacture tolerance and to improve the device performance limited by a chip length by forming an optical waveguide element so as to allow the branching angle of an input/output optical waveguide to be an angle equal to or less than a specified value.

A reflector 6 is formed at the end of a merged optical waveguide 8 for which two single mode input/output optical waveguides formed on a substrate 7 are merged and united. Along with that, at the time of defining a total reflection complementary angle by the refractive index difference of the waveguide and the substrate 7 as θc, the formation is performed so as to allow the branching angle of the input/output optical waveguide to be the angel equal to or less than 0.55*θc. That is, in this element, the branching angle θ of the optical waveguide and the length of the merged waveguide (cross waveguide) 8 from the position of merging the optical waveguides to the reflector set to values for not returning to the waveguide on an incident side. Thus, since the element is miniaturized, integrated and formed, wide superiority is demonstrated for costs, functions, reliability and mass productivity, etc.