A Group III nitride semiconductor light-emitting device comprises a substrate (1) and a light-emitting layer (5) having the multiple quantum well structure that comprises barrier layers (5a) and well layers (5b) formed of a gallium-containing Group III nitride semiconductor material provided on the substrate. Each of the well layers constituting the multiple quantum well structure is made of a Group III nitride semiconductor layer to which acceptor impurities are added, and which has thicknesses different from one another and the same conductivity type as that of the barrier layer. The present invention can provide a Group III nitride semiconductor white light-emitting device which can enhance luminous intensity, can obtain high color rendering properties has a simple structure that can be easily formed without fine adjustment of a composition of a phosphor.