A nitride group semiconductor light emitting device comprising: a substrate, n-type and p-type semiconductor layers (11, 12) that are formed on or above said substrate, and an active region that is interposed between the n-type and p-type semiconductor layers (11, 12), the active region having a first active region and a second active region, wherein said active region includes barrier layers that are included in a multiquantum well structure, wherein said barrier layers include at least first barrier layers in the first active region, and second barrier layers in the second active region, the second barrier layers being arranged on the p-type semiconductor layer side relative to said first barrier layers, and having_a thickness smaller than said first barrier layers, wherein said p-type semiconductor layer is deposited on the barrier layer that has the smallest thickness among the thicknesses of the barrier layers that are included in said active region, wherein each of said first barrier layers has the same thickness, and each of said second barrier layers has the same thickness, wherein said active region includes well layers that are included in the multiquantum well structure, wherein said well layers include at least first well layers each of which has the same thickness, and second well layers each of which has the same thickness, wherein the thickness of said first barrier layers is about 1.1 to 2.0 times of the thickness of said second barrier layers, wherein the thickness of said second well layers of said second active region is equal to the thickness of said first well layers of said first active region, the total number of said first barrier layers is greater than the total of said second barrier layers, and the number of pairs of the first barrier layers and the first well layers is twice or more than the number of pairs of the second barrier layers and the second well layers. a substrate, n-type and p-type semiconductor layers (11, 12) that are formed on or above said substrate, and an active region that is interposed between the n-type and p-type semiconductor layers (11, 12), the active region having a first active region and a second active region, wherein said active region includes barrier layers that are included in a multiquantum well structure, wherein said barrier layers include at least first barrier layers in the first active region, and second barrier layers in the second active region, the second barrier layers being arranged on the p-type semiconductor layer side relative to said first barrier layers, and having_a thickness smaller than said first barrier layers, wherein said p-type semiconductor layer is deposited on the barrier layer that has the smallest thickness among the thicknesses of the barrier layers that are included in said active region, wherein each of said first barrier layers has the same thickness, and each of said second barrier layers has the same thickness, wherein said active region includes well layers that are included in the multiquantum well structure, wherein said well layers include at least first well layers each of which has the same thickness, and second well layers each of which has the same thickness, wherein the thickness of said first barrier layers is about 1.1 to 2.0 times of the thickness of said second barrier layers, wherein the thickness of said second well layers of said second active region is equal to the thickness of said first well layers of said first active region, the total number of said first barrier layers is greater than the total of said second barrier layers, and the number of pairs of the first barrier layers and the first well layers is twice or more than the number of pairs of the second barrier layers and the second well layers.