A lighting device comprising: a heat sink (300") including a first heat radiation part (310") and a second heat radiation part (330"); a light source module including a substrate disposed on the heat sink (300") and a light emitting device disposed on the substrate; and a power supply unit which is disposed within the second heat radiation part (330") of the heat sink (300") and supplies power to the light source module, wherein the second heat radiation part (330") of the heat sink (300") comprises an inner portion (331") receiving the power supply unit therewithin, an outer portion (335") enclosing the inner portion (331"), and a first receiver (333") disposed between the inner portion (331") and the outer portion (335"), wherein the first heat radiation part (310") of the heat sink (300") comprises an upper portion (311") which is disposed on the top of the lower portion of the first heat radiation part, and a lower portion disposed in the first receiver (333") of the second heat radiation part (330"), characterized in that: the top of the lower portion of the first heat radiation part is opened, the upper portion of the first heat radiation part is not disposed in a top opening of the lower portion, but extends outwardly from the top of the lower portion, such that said upper portion is disposed on the top part of the outer portion (335") of the second heat radiation part (330"), the entire top surface of the inner portion (331") of the second heat radiation part(330") is exposed through the top opening of the lower portion of the first heat radiation part. a heat sink (300") including a first heat radiation part (310") and a second heat radiation part (330"); a light source module including a substrate disposed on the heat sink (300") and a light emitting device disposed on the substrate; and a power supply unit which is disposed within the second heat radiation part (330") of the heat sink (300") and supplies power to the light source module, wherein the second heat radiation part (330") of the heat sink (300") comprises an inner portion (331") receiving the power supply unit therewithin, an outer portion (335") enclosing the inner portion (331"), and a first receiver (333") disposed between the inner portion (331") and the outer portion (335"), wherein the first heat radiation part (310") of the heat sink (300") comprises an upper portion (311") which is disposed on the top of the lower portion of the first heat radiation part, and a lower portion disposed in the first receiver (333") of the second heat radiation part (330"), characterized in that: the top of the lower portion of the first heat radiation part is opened, the upper portion of the first heat radiation part is not disposed in a top opening of the lower portion, but extends outwardly from the top of the lower portion, such that said upper portion is disposed on the top part of the outer portion (335") of the second heat radiation part (330"), the entire top surface of the inner portion (331") of the second heat radiation part(330") is exposed through the top opening of the lower portion of the first heat radiation part. wherein the second heat radiation part (330") of the heat sink (300") comprises an inner portion (331") receiving the power supply unit therewithin, an outer portion (335") enclosing the inner portion (331"), and a first receiver (333") disposed between the inner portion (331") and the outer portion (335"), wherein the first heat radiation part (310") of the heat sink (300") comprises an upper portion (311") which is disposed on the top of the lower portion of the first heat radiation part, and a lower portion disposed in the first receiver (333") of the second heat radiation part (330"), characterized in that: the top of the lower portion of the first heat radiation part is opened, the upper portion of the first heat radiation part is not disposed in a top opening of the lower portion, but extends outwardly from the top of the lower portion, such that said upper portion is disposed on the top part of the outer portion (335") of the second heat radiation part (330"), the entire top surface of the inner portion (331") of the second heat radiation part(330") is exposed through the top opening of the lower portion of the first heat radiation part. the top of the lower portion of the first heat radiation part is opened, the upper portion of the first heat radiation part is not disposed in a top opening of the lower portion, but extends outwardly from the top of the lower portion, such that said upper portion is disposed on the top part of the outer portion (335") of the second heat radiation part (330"), the entire top surface of the inner portion (331") of the second heat radiation part(330") is exposed through the top opening of the lower portion of the first heat radiation part.