A second-harmonic generation device includes a semiconductor laser element which has a quantum-well active layer, a wavelength control means which controls the wavelength of the light emitted from an end facet of the semiconductor laser element, an optical system which returns to the semiconductor laser element the light the wavelength of which is controlled by the wavelength control means, and a wavelength conversion element which is directly coupled to the other end facet of the semiconductor laser element, and converts the wavelength of the light controlled by the wavelength control means, to a half wavelength. The semiconductor laser element has a resonator length equal to or greater than 900 micrometers and a mirror loss equal to or greater than 16 cm^-1.