A light emitting diode including a compound semiconductor layer having at least a pn junction-type light emitting unit and a strain adjustment layer stacked on the light emitting unit, wherein the light emitting unit has a stacked structure containing a strained light emitting layer having a composition formula of (AlXGa1-X)YIn1-YP (wherein X and Y are numerical values that satisfy 0≦X≦0.1 and 0.39≦Y≦0.45 respectively) and a barrier layer, and the strain adjustment layer is transparent to the emission wavelength and has a lattice constant that is smaller than the lattice constants of the strained light emitting layer and the barrier layer. The light emitting diode has an emission wavelength of not less than 655 nm, exhibits excellent monochromaticity, high output and/or high efficiency, and has a fast response speed.