A nitride semiconductor laser device has a semiconductor multi-layer structure that includes a lower clad layer of a first conductive type, an active layer, and an upper clad layer of a second conductive type stacked in this order on a substrate, wherein a layer under the active layer includes a stripe-like trench; the semiconductor multi-layer structure includes a stripe-like optical cavity arranged along the stripe-like trench; the stripe-like trench has a narrower width in its both end regions compared to its central main region; and the active layer is formed of a nitride semiconductor containing In.