A Group III nitride semiconductor light-emitting device includes a stacked structure 11 formed on a crystal substrate (100) to be removed from it and including two Group III nitride semiconductor layers 104 and 106 having different electric conductive types and a light-emitting layer 105 which is stacked between the two Group III nitride semiconductor layers and which includes a Group III nitride semiconductor, and a plate body 111made of material different from that of the crystal substrate and formed on a surface of an uppermost layer which is opposite from the crystal substrate that is removed from the stacked structure.