An air conditioner comprising: an outdoor portion of the air conditioner including a heat exchanger (40, 40') and a fan assembly disposed at an upper portion of the heat exchanger (40, 40'), wherein the heat exchanger (40, 40') includes: a first heat exchanger unit (41, 41a) disposed adjacent to the fan assembly; and a second heat exchanger unit (42, 42a) disposed vertically under the first heat exchanger unit (41, 41a), wherein each of the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a) includes: a plurality of layers (46, 47, 48) including a first layer; a second layer disposed inside of the first layer with respect to an airflow direction into the outdoor portion; and a third layer disposed inside of the second layer with respect to the airflow direction, wherein each layer (46, 47, 48) includes: a plurality of refrigerant tubes (460, 461, 470, 471, 480, 481); and at least one fin assembly (463, 473, 474, 483, 484) configured with fins having different fin pitches and different shapes, wherein a first refrigerant tube of the first layer is connected to a first refrigerant tube and a second refrigerant tube of the second layer at one end of the heat exchanger (40, 40'), wherein the first heat exchanger unit (41, 41a) includes at least one fin assembly configured with a high-speed fin having a fin pitch and a fin shape adapted to high-speed airflow, and the second heat exchanger unit (42, 42a) includes at least one fin assembly configured with a low-speed fin having a fin pitch and a fin shape adapted to low-speed airflow, wherein the first layer includes one uniform fin assembly disposed vertically to correspond to the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a); and each of the second layer and the third layer includes two fin assemblies (473, 474, 483, 484) disposed vertically to correspond, respectively, to the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a), wherein the fin assemblies (473, 483) disposed at the second layer and the third layer of the first heat exchanger unit (41, 41a) are configured with high-speed fins having the fin pitch and the fin shape which are advantageous to a high-speed air flow, the fin assemblies (474, 484) disposed at the second layer and the third layer of the second heat exchanger unit (42, 42a) are configured with low-speed fins having the fin pitch and the fin shape which are advantageous to a low-speed air flow, and wherein the fin pitch of the fin assemblies (473, 483) disposed at the second layer and the third layer of the first heat exchanger unit (41, 41a) is smaller than the fin pitch of the uniform fin assembly disposed at the first layer of the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a). an outdoor portion of the air conditioner including a heat exchanger (40, 40') and a fan assembly disposed at an upper portion of the heat exchanger (40, 40'), wherein the heat exchanger (40, 40') includes: a first heat exchanger unit (41, 41a) disposed adjacent to the fan assembly; and a second heat exchanger unit (42, 42a) disposed vertically under the first heat exchanger unit (41, 41a), wherein each of the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a) includes: a plurality of layers (46, 47, 48) including a first layer; a second layer disposed inside of the first layer with respect to an airflow direction into the outdoor portion; and a third layer disposed inside of the second layer with respect to the airflow direction, wherein each layer (46, 47, 48) includes: a plurality of refrigerant tubes (460, 461, 470, 471, 480, 481); and at least one fin assembly (463, 473, 474, 483, 484) configured with fins having different fin pitches and different shapes, wherein a first refrigerant tube of the first layer is connected to a first refrigerant tube and a second refrigerant tube of the second layer at one end of the heat exchanger (40, 40'), wherein the first heat exchanger unit (41, 41a) includes at least one fin assembly configured with a high-speed fin having a fin pitch and a fin shape adapted to high-speed airflow, and the second heat exchanger unit (42, 42a) includes at least one fin assembly configured with a low-speed fin having a fin pitch and a fin shape adapted to low-speed airflow, wherein the first layer includes one uniform fin assembly disposed vertically to correspond to the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a); and each of the second layer and the third layer includes two fin assemblies (473, 474, 483, 484) disposed vertically to correspond, respectively, to the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a), wherein the fin assemblies (473, 483) disposed at the second layer and the third layer of the first heat exchanger unit (41, 41a) are configured with high-speed fins having the fin pitch and the fin shape which are advantageous to a high-speed air flow, the fin assemblies (474, 484) disposed at the second layer and the third layer of the second heat exchanger unit (42, 42a) are configured with low-speed fins having the fin pitch and the fin shape which are advantageous to a low-speed air flow, and wherein the fin pitch of the fin assemblies (473, 483) disposed at the second layer and the third layer of the first heat exchanger unit (41, 41a) is smaller than the fin pitch of the uniform fin assembly disposed at the first layer of the first heat exchanger unit (41, 41a) and the second heat exchanger unit (42, 42a).