A semiconductor light-emitting element has a GaN type green LED, and a wavelength selecting element which selects and outputs only predetermined wavelength components. The wavelength selecting element is formed by an interference filter or an etalon, and selects and outputs only wavelength components of 520 nm or less from green light emitted by the GaN type green LED. If it is desired to make a response speed even faster, the wavelength selecting element may select and output only wavelengths at a shorter wavelength side of a central wavelength of an emission spectrum (i.e., wavelengths of 515 nm or less).