An organic light emitting device comprising: a first stack emission unit including a first hole transporting layer, a first emitting layer, and a first electron transporting layer; a second stack emission unit including a second hole transporting layer, a second emitting layer, and a second electron transporting layer; and a first charge generating layer between the first stack emission unit and the second stack emission unit, wherein the first charge generating layer includes an N-type charge generating layer configured to inject electrons into the first stack emission unit and a P-type charge generating layer, which is a non-doped organic layer and configured to inject holes into the second stack emission unit, the P-type charge generating layer and the second hole transporting layer are in direct contact with each other, and a difference between a lowest unoccupied molecular orbital (LUMO) energy level of the P-type charge generating layer and a highest occupied molecular orbital (HOMO) energy level of the second hole transporting layer is smaller than a difference between a HOMO energy level of the P-type charge generating layer and the HOMO energy level of the second hole transporting layer, characterized in that the P-type charge generating layer consists of a host material selected from the group consisting of NPD (N,N-dinaphthyl-N,N'-diphenyl benzidine)(N,N'-bis(naphthalene-l-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine), TPD (N,N'-bis-(3-methylphenyl)-N,N'-bis-(phenyl)-benzidine), and MTDATA (4,4',4-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine), the second hole transporting layer is formed of a material selected from the group consisting of PY1 (3,5-di(pyren-l-yl)pyridine, TmPPPyTz (2,4,6-tris(3'-(pyridine-3-yl)biphenyl-3-yl)-l,3,5-triazine), TAZ (3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole) or BPhen (4,7-diphenyl-l,10-phenanthroline), wherein the material for the host material in the P-type charge generating layer and the material for the second hole transporting layer is selected such that the difference between the LUMO energy level of the P-type charge generating layer and the HOMO energy level of the second hole transporting layer is smaller than 0.15 eV in absolute value. a second stack emission unit including a second hole transporting layer, a second emitting layer, and a second electron transporting layer; and a first charge generating layer between the first stack emission unit and the second stack emission unit, wherein the first charge generating layer includes an N-type charge generating layer configured to inject electrons into the first stack emission unit and a P-type charge generating layer, which is a non-doped organic layer and configured to inject holes into the second stack emission unit, the P-type charge generating layer and the second hole transporting layer are in direct contact with each other, and a difference between a lowest unoccupied molecular orbital (LUMO) energy level of the P-type charge generating layer and a highest occupied molecular orbital (HOMO) energy level of the second hole transporting layer is smaller than a difference between a HOMO energy level of the P-type charge generating layer and the HOMO energy level of the second hole transporting layer, characterized in that the P-type charge generating layer consists of a host material selected from the group consisting of NPD (N,N-dinaphthyl-N,N'-diphenyl benzidine)(N,N'-bis(naphthalene-l-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine), TPD (N,N'-bis-(3-methylphenyl)-N,N'-bis-(phenyl)-benzidine), and MTDATA (4,4',4-Tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine), the second hole transporting layer is formed of a material selected from the group consisting of PY1 (3,5-di(pyren-l-yl)pyridine, TmPPPyTz (2,4,6-tris(3'-(pyridine-3-yl)biphenyl-3-yl)-l,3,5-triazine), TAZ (3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole) or BPhen (4,7-diphenyl-l,10-phenanthroline), wherein the material for the host material in the P-type charge generating layer and the material for the second hole transporting layer is selected such that the difference between the LUMO energy level of the P-type charge generating layer and the HOMO energy level of the second hole transporting layer is smaller than 0.15 eV in absolute value.