Provided is a group-III nitride semiconductor light-emitting device which has a high level of crystallinity and superior internal quantum efficiency and which is capable of enabling acquisition of high level light emission output, and a manufacturing method thereof, and a lamp. An AlN seed layer composed of a group-III nitride based compound is laminated on a substrate 11, and on this AlN seed layer, there are sequentially laminated each layer of an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer respectively composed of a group-III nitride semiconductor, wherein the full width at half-maximum of the X-ray rocking curve of the (0002) plane of the p-type semiconductor layer 16 is 60 arcsec or less, and the full width at half-maximum of the X-ray rocking curve of the (10-10) plane is 250 arcsec or less.