A multi-beam generating device has plural semiconductor lasers, optical fibers to propagate laser beams generated by the semiconductor lasers, an optical fiber array to propagate the laser beams passed through the optical fibers, and an optical waveguide device provided with waveguides to propagate the laser beams having passed through the optical fiber array. Each of the waveguides has a core layer and a clad layer; a pitch between adjacent waveguides in the arrangement is narrower on the output section side where the laser beams emit than on the input section side where the laser beams enter; a width of the core layer is narrower in the transverse direction that is the direction of the arrangement of the waveguides than in the vertical direction; and a difference in refractive index between the core layer and the clad layer is larger in the transverse direction than in the vertical direction.