A light emitting device comprising: a light emitting structure including a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer including at least one combination of a well layer of a first composition formed of a nitride-semiconductor material having first electronic energy and a barrier layer of a second composition formed of a nitride-semiconductor material having higher electronic energy than the first electronic energy between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer; and an interface layer disposed between the second conductivity-type semiconductor layer and the active layer or between the first conductivity-type semiconductor layer and the active layer, wherein: the interface layer includes a first layer, a second layer and a third layer having different energy bandgaps, the energy bandgaps of the first layer and the second layer are greater than the energy bandgap of the barrier layer in the active layer, and the energy bandgap of the third layer is less than the energy bandgap of the barrier layer in the active layer, characterized in that the energy bandgap of the first layer is greater than the energy bandgap of the second layer, and an in-plane lattice constant of at least one of the first layer, the second layer and the third layer is greater than an in-plane lattice constant of the barrier layer in the active layer. a light emitting structure including a first conductivity-type semiconductor layer, a second conductivity-type semiconductor layer, and an active layer including at least one combination of a well layer of a first composition formed of a nitride-semiconductor material having first electronic energy and a barrier layer of a second composition formed of a nitride-semiconductor material having higher electronic energy than the first electronic energy between the first conductivity-type semiconductor layer and the second conductivity-type semiconductor layer; and an interface layer disposed between the second conductivity-type semiconductor layer and the active layer or between the first conductivity-type semiconductor layer and the active layer, wherein: the interface layer includes a first layer, a second layer and a third layer having different energy bandgaps, the energy bandgaps of the first layer and the second layer are greater than the energy bandgap of the barrier layer in the active layer, and the energy bandgap of the third layer is less than the energy bandgap of the barrier layer in the active layer, characterized in that the energy bandgap of the first layer is greater than the energy bandgap of the second layer, and an in-plane lattice constant of at least one of the first layer, the second layer and the third layer is greater than an in-plane lattice constant of the barrier layer in the active layer. the interface layer includes a first layer, a second layer and a third layer having different energy bandgaps, the energy bandgaps of the first layer and the second layer are greater than the energy bandgap of the barrier layer in the active layer, and the energy bandgap of the third layer is less than the energy bandgap of the barrier layer in the active layer, characterized in that the energy bandgap of the first layer is greater than the energy bandgap of the second layer, and an in-plane lattice constant of at least one of the first layer, the second layer and the third layer is greater than an in-plane lattice constant of the barrier layer in the active layer.