A coupling structure of waveguide including a line defect (LD) waveguide portion having an LD waveguide, an electromagnetic field distribution matching portion (EFDMP) connected between the LD waveguide portion and a first tapered portion, the first tapered portion connected with the EFDMP, and a thin line waveguide portion connected with the first tapered portion and having a thin line waveguide. The EFDMP has a matching portion LD as the LD of a columnar photonic crystal, and the matching portion LD is connected with the LD waveguide. The first tapered portion consists of a first thin wire core, and the first LD of a columnar photonic crystal arranged along at least one side of first thin line core. At least one of the first thin line core and the first LD is connected with the matching portion line defect. The thin line waveguide is connected with the first thin line core.