A quantum cascade laser includes: a substrate including a substrate end face; a semiconductor laminate having a laminate end face and a core extending in an axial direction; a first electrode disposed on the semiconductor laminate; a second electrode disposed on a back surface of the substrate; an insulating film disposed on the laminate end face and the first electrode; and a first metal film disposed on the laminate end face, the insulating film and the first electrode, the insulating film being between the first metal film and the semiconductor laminate. The substrate end face and the laminate end face extend along a reference plane intersecting the axial direction. The substrate end face has a first area and a second area arranged in a direction from the back surface to a principal surface of the substrate, and the first metal film has an end on the second area.