To solve the wavelength dependence of loss uniformity between waveguides for output. A waveguide for input for introducing an optical signal, a slab waveguide for branching off the optical signal introduced in the waveguide for input by diffraction and propagating, and a plurality of waveguides for output for outputting individually a plurality of optical signals which are branched off inside of the slab waveguide are provided. The waveguide for input is configured such that an output end thereof is connected to an incident end of the slab waveguide and has a function for converting a spot size of the optical signal on the incident end of the slab waveguide at a connection point with the slab waveguide.