[PROBLEM] To manufacture a quantum cascade laser (QCL) element having a reduced threshold current density (Jth) and an increased maximum operating temperature (Tmax).[SOLUTION] One embodiment of the present invention provides a THz-QCL element (1000) with a QCL structure (100), which is a semiconductor superlattice (100A) sandwiched between a pair of electrodes (20, 30). The semiconductor superlattice (100A) (QCL structure (100)) is provided with an active region (10) that emits THz range electromagnetic waves due to the transition of electrons between sub-bands during application of a voltage to the pair of electrodes, for example. The active region (10) has repeating unit structures (10U) of a thickness, which includes sets of a well layer (10W) and a barrier layer (10B) alternatingly laminated with each other, wherein the well layer (10W) is made of AlxGa1-xAs (where 0