An object of the invention is to prevent migration of silver contained in an electrode of a Group III nitride-based compound semiconductor light-emitting device. A positive electrode is formed on a p-type layer. In the positive electrode, an ITO light-transmitting electrode layer, a silver alloy reflecting electrode layer, a diffusion-preventing layer in which a Ti layer and a Pt layer are stacked, and a gold thick-film electrode are sequentially stacked on the p-type layer. The reflecting electrode layer made of a silver alloy contains palladium (Pd) and copper (Cu) as additives and also contains oxygen (O). By virtue of this structure, migration of silver from the silver alloy reflecting electrode layer and blackening of the interface between the silver alloy layer and the ITO light-transmitting electrode layer disposed thereunder are prevented, whereby light extraction efficiency can be enhanced.