A quantum cascade laser includes a semiconductor substrate, and an active layer being provided on the substrate, and having a cascade structure in which quantum well emission layers and injection layers are alternately laminated, and the laser has a base portion including the substrate, and a stripe-shaped ridge portion including the active layer. Further, a reflection control film is formed from a ridge end face over a base end face on an end face in a resonating direction of the laser, and, on the base end face, for a second side and a third side adjacent to a first side on the ridge portion side of the base end face, and a fourth side facing the first side, the reflection control film is formed on a region other than regions near those three sides with predetermined widths.