In a GaN-based laser device having a GaN-based semiconductor stacked-layered structure including a light emitting layer, the semiconductor stacked-layered structure includes a ridge stripe structure causing a stripe-shaped waveguide, and has side surfaces opposite to each other to sandwich the stripe-shaped waveguide in its width direction therebetween. At least part of at least one of the side surfaces is processed to prevent the stripe-shaped waveguide from functioning as a Fabry-Perot resonator in the width direction.