An optical waveguide coupler for optically coupling an optical waveguide and an optical component having mutually different spot sizes, includes (1) a first spot size converting part, placed on the optical waveguide side, that converts a spot size with higher efficiency for an optical signal of a long wavelength band than for an optical signal of a short wavelength band, and (2) a second spot size converting part, placed on the optical component side, that converts a spot size with higher efficiency for the optical signal of the short wavelength band than for the optical signal of the long wavelength band.