A light emitting device including a III-V group compound semiconductor includes a first stacked body and a second stacked body. The first stacked body includes a III-V group compound semiconductor stacked body, and a reflection layer, a first diffusion suppressing layer and a first metal layer formed on one main surface of the III-V group compound semiconductor stacked body. The second stacked body includes a semiconductor substrate and a second metal layer. The first stacked body and the second stacked body are joined by the first metal layer and the second metal layer, and by the first diffusion suppressing layer, diffusion of atoms between the reflection layer and the first metal layer is suppressed. Therefore, a III-V group compound semiconductor device having high efficiency of light emission to the outside per chip and manufacturing method thereof can be provided.