According to one embodiment, a light emitting device and a luminaire with high heat radiation property are provided. The light-emitting device includes a light-emitting section, a thermal radiation member, and a heat conduction layer. The light-emitting section includes a mounting substrate section and a light-emitting element section. The mounting substrate section includes a substrate, a first metal layer, and a second metal layer. The substrate includes a first principal plane including a mounting region, and a second principal plane, and is insulative. The first metal layer is disposed on the first principal plane and includes mounting patterns disposed in the mounting region. The second metal layer is disposed on the second principal plane and is insulative with the first metal layer. The light-emitting element section includes semiconductor light-emitting elements and a wavelength conversion layer. The semiconductor light-emitting elements are connected to the mounting patterns. The luminous exitance of the light-emitting element section is equal to or higher than 101 m/mm2 and equal to or lower than 1001 m/mm2. The thermal radiation member faces the second principal plane and has an area equal to or larger than five times the area of the mounting region. The heat conduction layer is disposed between the heat radiation member and the second metal layer.