Abstract: A three-dimensional photonic crystal having a wide and sharp bandgap, a manufacturing method thereof, a structural body for manufacturing this photonic crystal, and a manufacturing method thereof are provided. The structural body is formed by placing monodisperse particles in a recess having a regular quadrangular pyramid shape formed in a container, arranging the particles three-dimensionally by applying vibration, and performing sintering, so that adjacent particles are connected to each other with necks provided therebetween. A dielectric resin is impregnated in voids of the structural body and is then cured to form a composite. The composite is immersed in a solution which dissolves only the structural body. Monodisperse particles exposed at the surface of the composite are dissolved, and monodisperse particles adjacent thereto with necks provided therebetween are then sequentially dissolved, so that the whole structural body is finally dissolved.