A cascade laser device, including a multilayer film structure with a multiple quantum well including a potential barrier and a quantum well; and an electric field applying portion for applying an electric field to the multilayer film structure. The multilayer film structure includes at least two first regions and a second region. The second region is sandwiched between the two first regions; each of the first regions includes multiple sub-bands. When the electric field is applied, carriers are transported from a sub-band in the higher energy quantum well to a sub-band in the lower energy quantum well via the potential barrier in the first regions by tunneling permitted by interaction with light. The second region is thinner than twice a skin depth of the light and includes at least a film having an energy band. The carriers are subjected to energy relaxation in the energy band.