A two-dimensional photonic crystal, wherein on a plane in which four adjoining unit lattices L are arranged so as to have one angle in common with the unit lattice L being a rectangle whose shorter side X1 has a length of x1 and whose longer side Y1 has a length of y1, columnar first dielectric regions each having a rectangular cross section whose shorter side X2 has a length of x2 and whose longer side Y2 has a length of y2 are arranged on shorter sides X1 and longer sides Y1 of each rectangular unit lattice L. In this two-dimensional photonic crystal, the first dielectric region is arranged so that the midpoint of the shorter side X1 and the midpoint of the longer side Y1 and the center of the rectangular cross section substantially coincide, and longer sides Y2 of each first dielectric region are substantially parallel to each other.