To provide a superluminescent diode capable of emitting high output super luminescent light having a central wavelength within a range of 0.95 .mu.m to 1.2 .mu.m and an undistorted beam cross section, having a long element life. The super luminescent diode is constituted by: an n-type GaAs substrate; an optical waveguide path constituted by an InGaAs active layer that emits light having a central wavelength within a range of 0.95 .mu.m to 1.2 .mu.m, formed on the GaAs substrate; and a window region layer having a greater energy gap and a smaller refractive index than the active layer, constituted by p-type GaAs that lattice matches with the GaAs substrate, provided at a rear emitting facet of the optical waveguide path. The p-type GaAs window region layer has a favorable crystal membrane with the InGaAs active layer that emits light having the central wavelength within the range of 0.95 .mu.m to 1.2 .mu.m, which does not deteriorate.