This gallium nitride-based compound semiconductor light emitting device includes an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer that are composed of gallium nitride-based compound semiconductors and are deposited in that order on a substrate, and further includes a negative electrode and a positive electrode that are in contact with the n-type semiconductor layer and the p-type semiconductor layer, respectively, wherein the positive electrode has a translucent electrode composed of a three-layer structure including a contact metal layer that contacts at least the p-type semiconductor layer, a current diffusion layer provided on the contact metal layer and having conductivity greater than that of the contact metal layer, and a bonding pad layer provided on the current diffusion layer, and a mixed positive electrode-metal layer including a metal that forms the contact metal layer is present in a positive electrode side surface of the p-type semiconductor layer.