A semiconductor laser device which comprises a laser diode chip (100) that emits laser light; a 45° reflective mirror (400) that changes laser light traveling horizontally to a package bottom into laser light traveling perpendicular to the package bottom. The 45° reflective mirror (400) is a partial reflective mirror which has a partial reflection/partial transmission characteristic. An optical feedback-partial reflective mirror (500) is disposed along a path of light passing vertically through the 45° reflective mirror (400). The optical feedback-partial reflective mirror (500) supplies some of the laser light traveling through the 45° reflective mirror (400) back to the 45° reflective mirror 400 by reflecting a first portion of the laser light while transmitting a remaining portion of the laser light.