A nitride semiconductor laser diode includes: a substrate made of silicon in which a plane orientation of a principal surface is a {100} plane; and a semiconductor that includes a plurality of semiconductor layers formed on the substrate and including an active layer, each of the plurality of semiconductor layers being made of group III nitride. The semiconductor has a plane parallel to a {011} plane which is a plane orientation of silicon as a cleaved facet, the cleaved facet forming a facet mirror.