An outdoor heat exchanger configured to function as a condenser in an air cooling operation and as an evaporator in an air heating operation, the outdoor heat exchanger comprising: a first header pipe configured to have a refrigerant, compressed by a compressor, to flow therein in the air cooling operation; a first heat exchange unit coupled to the first header pipe and including a plurality of refrigerant tubes and a plurality of electric heat pins to thermally exchange the refrigerant with air; a bypass pipe configured to have the refrigerant, thermally exchanged in the first heat exchange unit, to flow therein in the air cooling operation; a first distribution pipe coupled to the bypass pipe; a second header pipe configured to have the refrigerant, passing through the bypass pipe, to flow therein in the air cooling operation; a second heat exchange unit coupled to the second header pipe and including a plurality of refrigerant tubes and a plurality of electric heat pins to thermally exchange the refrigerant with air; a second distribution pipe configured to have the refrigerant, thermally exchanged in the second heat exchange unit, to flow therein in the air cooling operation; a second hot gas pipe configured to couple the compressor and the second distribution pipe; and a second hot gas control valve disposed in the second hot gas pipe to control a flow of the refrigerant, characterised in that the first heat exchange unit and the second heat exchange unit are vertically disposed and share the plurality of electric heat pins, and the second heat exchange unit condenses the refrigerant, condensed by the first heat exchange unit, again in the air cooling operation, the outdoor heat exchanger further comprises a bypass valve disposed in the bypass pipe and opened or closed in order to control the flow of the refrigerant, wherein the bypass valve is opened in the air cooling operation, and the second hot gas control valve is opened, the bypass valve is closed, and the refrigerant compressed by the compressor flows in the second heat exchange unit to heat the second heat exchange unit in a partial defrosting operation, and the first heat exchange unit evaporates the refrigerant in the partial defrosting operation. a first header pipe configured to have a refrigerant, compressed by a compressor, to flow therein in the air cooling operation; a first heat exchange unit coupled to the first header pipe and including a plurality of refrigerant tubes and a plurality of electric heat pins to thermally exchange the refrigerant with air; a bypass pipe configured to have the refrigerant, thermally exchanged in the first heat exchange unit, to flow therein in the air cooling operation; a first distribution pipe coupled to the bypass pipe; a second header pipe configured to have the refrigerant, passing through the bypass pipe, to flow therein in the air cooling operation; a second heat exchange unit coupled to the second header pipe and including a plurality of refrigerant tubes and a plurality of electric heat pins to thermally exchange the refrigerant with air; a second distribution pipe configured to have the refrigerant, thermally exchanged in the second heat exchange unit, to flow therein in the air cooling operation; a second hot gas pipe configured to couple the compressor and the second distribution pipe; and a second hot gas control valve disposed in the second hot gas pipe to control a flow of the refrigerant, characterised in that the first heat exchange unit and the second heat exchange unit are vertically disposed and share the plurality of electric heat pins, and the second heat exchange unit condenses the refrigerant, condensed by the first heat exchange unit, again in the air cooling operation, the outdoor heat exchanger further comprises a bypass valve disposed in the bypass pipe and opened or closed in order to control the flow of the refrigerant, wherein the bypass valve is opened in the air cooling operation, and the second hot gas control valve is opened, the bypass valve is closed, and the refrigerant compressed by the compressor flows in the second heat exchange unit to heat the second heat exchange unit in a partial defrosting operation, and the first heat exchange unit evaporates the refrigerant in the partial defrosting operation.