A three-dimensional photonic crystal includes a structure that includes first, second, third, and fourth layers in this order. The structure of each layer includes a flat surface as one end surface, and first, second, and third structural portions. The first structural portion has a first width along the flat surface and a first height from the flat surface. The second structural portion has a second width larger than the first width and a second height larger than the first height. The third structural portion has a width and a height that continuously or stepwise change in the extending direction of the structure. The flat surface at the structural portion of one of two adjacent layers in the first layer to the fourth layer contacts a surface opposite to the flat surface at the second structural portion of the other of the two adjacent layers.