A nitride group semiconductor light emitting device includes a substrate, n-type and p-type semiconductor layers, and an active region. The n-type and p-type semiconductor layers are formed on or above the substrate. The active region is interposed between the n-type and p-type semiconductor layers. The active region includes barrier layers that are included in a multiquantum well structure, and an end barrier layer that has a thickness greater than the barrier layer, and is arranged closest to the p-type semiconductor layer. The average thickness of the last two barrier layers that are arranged adjacent to the end barrier layer is smaller than the average thickness of the other barrier layers among the thicknesses of the barrier layers that are included in the multiquantum well structure.