The object of the present invention is to provide a method of manufacturing a Group-III nitride semiconductor light-emitting device that is highly productive and that enables production of a device having excellent light-emitting properties; a Group-III nitride semiconductor light-emitting device; and a lamp using the light emitting device. The present invention provides a method of manufacturing a Group-III nitride semiconductor light-emitting device, comprising the steps of: activating a gas including a Group-V element and a metal material with plasma, thereby reacting the gas with the metal material; forming on a substrate an intermediate layer that is made of a Group-III nitride compound; and stacking an n-type semiconductor layer that is made of a Group-III nitride semiconductor, a light-emitting layer, and a p-type semiconductor layer, sequentially on the intermediate layer, wherein the Group-V element is nitrogen, the gas fraction of nitrogen in the gas is within a range of more than 20% to less than 99% during forming of the intermediate layer, and the intermediate layer is formed into a single crystal structure.