To prevent emission efficiency drop and deterioration of reliability of product due to fluctuation of the emission efficiency by forming a nitride semiconductor film on a substrate, making recesses and protrusions in the grown surface of the substrate, and making a cavity between the nitride semiconductor film and the substrate in the recess.

A machining structure substrate (substrate) 1O0 has grooves 115 and protrusions (flat parts) 114 appearing on the surface of the substrate 100 upon formation of the grooves 115. A nitride semiconductor film is formed on the substrate 100. In addition to a nitride semiconductor film 123 formed on the protrusions 114, a nitride semiconductor film 124 is formed on the grooves 115 and a cavity 116 nor formed with the nitride semiconductor film is present in the grooves 115. Furthermore, a nitride semiconductor film 125 is deposited on the bottom of the grooves 115. The nitride semiconductor film 123 formed on the protrusions 114 can relax stress generated between the nitride semiconductor film 124 and the substrate 100 by means of the nitride semiconductor film 124 not influenced by the substrate 100.