To provide a compound semiconductor element in which light at a specific wavelength contributes largely by a method in which the compound semiconductor element is composed of a compound semiconductor having a region in which a change in the thickness direction in a composition ratio is a parabolic function shape.

For example, in an AlxGa1-xAs system, the composition of a barrier layer Al at both ends of a parabola is set at 0.45, and the composition of the Al in the position of the vortex of the parabola, i.e., at the bottom of a quantum well, is set at x=0. The width of the parabola is formed so as to become 44 ML (a monoatomic layer, 1 ML=0.283nm). At this time, (x) is changed continuously in such a way that a potential shape becomes a parabola. In a quantum well structure whose potential shape is a parabolic function shape, electrons are transited up to a high level while they are emitting light in an avalanche shape from a high-order excitation level down to a base level. At this time, wavelengths of light emitted due to their transition between respective levels are all equal. As a result, the intensity of the light emitted as a whole can be expressed as the sum of intensities of light emissions due to the transition between the respective levels, and light at a specific wavelength can contribute largely.