The present invention provides a Group III nitride semiconductor light-emitting device which is intended to relax stress applied to a light-emitting layer. The light-emitting device includes an MQW layer, and an n-side superlattice layer formed below the MQW layer. The n-side superlattice layer is formed by repeatedly depositing layer units, each unit including an InGaN layer, a GaN layer, and an n-GaN layer which are sequentially deposited from the side of the sapphire substrate. In the n-side superlattice layer, an InGaN layer more proximal to the MQW layer has a higher In compositional proportion. The In compositional proportion of the InGaN layer (which is most proximal to the MQW layer) of the n-side superlattice layer is 70% to 100% of the In compositional proportion of the InGaN layer (which is most proximal to the n-side superlattice layer) of the MQW layer.