An optical waveguide circuit includes a first loss component for causing a diffraction loss of light propagating through an optical waveguide, and a second loss component provided at least one of before and after the first loss component, for causing a diffraction loss less than the diffraction loss in the first loss component to the light propagating through the optical waveguide. This enables the beam spot size of the lightwave launched into the first loss component to be magnified seemingly, and to reduce the radiation angle of the lightwave at the first loss component, thereby making it possible to reduce the excess loss involved in the propagation of the light through the optical waveguide.