A plurality of protrusions is formed on the C-plane substrate with a corundum structure. A base film made of a III-V compound semiconductor including Ga and N is formed on the surface of the substrate. The surface of the base film is flatter than the surface of the substrate. A light emitting structure including Ga and N is disposed on the base film. The protrusions are regularly arranged in a first direction that is tilted by less than 15 degrees with respect to the a-axis of the base film and in a second direction that is orthogonal to the first direction. Each protrusion has two first parallel sides tilted by less than 15 degrees relative to an m-axis and two second parallel sides tilted by less than 15 degrees relative to the a-axis. An interval between the two second sides is wider than an interval between the two first sides.