One facet of a nitride based semiconductor laser device is composed of a cleavage plane of (0001), and the other facet thereof is composed of a cleavage plane of (000 1). Thus, the one facet and the other facet are respectively a Ga polar plane and an N polar plane. A portion of the one facet and a portion of the other facet, which are positioned in an optical waveguide, constitute a pair of cavity facets. A first protective film including nitrogen as a constituent element is formed on the one facet. A second protective film including oxygen as a constituent element is formed on the other facet.