A structural body includes a sapphire underlying substrate; and a semiconductor layer of a group III nitride semiconductor disposed on the underlying substrate. An upper surface of the underlying substrate is a crystal surface tilted at an angle of 0.5° or larger and 4° or smaller with respect to a normal line of an a-plane which is orthogonal to an m-plane and belongs to a {11-20} plane group, from the m-plane which belongs to a {1-100} plane group.