There is provided a nitride semiconductor light emitting device including: n-type and p-type nitride semiconductor layers; an active layer disposed between the n-type and p-type nitride semiconductor layers; and an electron injection layer disposed between the n-type nitride semiconductor layer and the active layer. The electron injection layer has a multilayer structure, in which three or more layers having different energy band gaps are stacked, and the multilayer structure is repetitively stacked at least twice. At least one layer among the three or more layers has a reduced energy band gap in individual multilayer structures in a direction toward the active layer, and the layer having the lowest energy band gap has an increased thickness in individual multilayer structures in a direction toward the active layer.