An object of the present invention is to provide a two-dimensional photonic crystal which can be used for optical path changeover switches or the like to allow switching of a path. A first area 121 and a second area 122 provided with holes 131 and 132 having a difference in the period and size are created on a body 11, and a main waveguide 15 is formed to obliquely cross a boundary 14 between these areas. A branch waveguide 17 branched from the main waveguide 15 into the first area 121 side is also formed by using a crossing point between the main waveguide 15 and the boundary 14 as a starting point. The second area 122 is heated to change a refractive index of the body within the area, so that a frequency band which can be passed through the main waveguide 15 of the second area 122 is changed. Light having a specific frequency and propagated through the main waveguide 15 from the first area 121 side is switched to be extracted from the main waveguide 15 on the second area 122 side or to be extracted from the branch waveguide 17 without propagating the main waveguide 15 on the second area 122, in response to whether or not the heating is performed.