Disclosed is a nitride based III-V group compound semiconductor laser device of ridge waveguide type with an oscillation wavelength of about 410 nm which has a low driving voltage, a high half-width value &thgr;// of a FFP in a direction horizontal to a hetero interface, and a high kink level (i.e., good light output-injected current characteristics over the high-output range). This laser device is similar in structure to the related-art semiconductor laser device except for the current constricting layer formed in a ridge. It has a stacked film composed of an SiO2 film (600 Å thick) and an amorphous Si film (300 Å thick) which are formed on the SiO2 film by vapor deposition. The stacked film covers both sides of the ridge and a p-AlGaN cladding layer extending sideward from the base of the ridge. The SiO2 film and Si film have respective thicknesses which are established such that the absorption coefficient of fundamental horizontal lateral mode is larger than the absorption coefficient of primary horizontal lateral mode. This structure results in a higher kink level, while suppressing the high-order horizontal lateral mode, a larger effective refractive index difference &Dgr;n, and a larger value of &thgr;// without the necessity for reducing the ridge width.