A quantum cascade laser includes: a semiconductor substrate including principal and back surfaces; a semiconductor laminate having a laminate end face, the laminate end face and, the substrate end face extending along a reference plane intersecting a second direction that intersects the first direction; a first electrode disposed on the semiconductor laminate, the semiconductor laminate being disposed between the first electrode and the semiconductor substrate; a second electrode disposed on the back surface; a first insulating film disposed on the laminate end face, the substrate end face, and the first electrode; a metal film disposed on the first insulating film and the laminate end face, the substrate end face, and the first electrode; and a second insulating film disposed on the second electrode, and on the substrate end face, the metal film being disposed between the first insulating film and the second insulating film.