A monolithic multi-wavelength laser device according to the present invention comprises a substrate, a first-wavelength lasing part having a ridge portion and a second-wavelength lasing part having a ridge portion, while each of the first-wavelength lasing part and the second-wavelength lasing part includes current blocking layers consisting of semiconductor thin films covering the side surfaces of the ridge portion and extending toward at least partial regions of a plane linked with the bottom surface of the ridge portion and an insulation layer, covering the current blocking layers, consisting of an insulating dielectric thin film made of a material having a lower refractive index than the current blocking layers.