A pn junction type Group III nitride semiconductor light-emitting device 10 (11) of the present invention has a light-emitting layer 2 of multiple quantum well structure in which well layers 22 and barrier layers 21 including Group III nitride semiconductors are alternately stacked periodically between an n-type clad layer 105 and a p-type clad layer 107 which are formed on a crystal substrate and which include Group III nitride semiconductors, in which one end layer 21m of the light-emitting layer 2 is closest to and opposed to the n-type clad layer, and the other end layer 21n of the light-emitting layer 2 is closest to and opposed to the p-type clad layer, both the one and the other end layers are barrier layers, and the other end layer 21n is thicker than the barrier layer of the one end layer.