An air conditioner comprising: a first compressor which compresses a refrigerant; a second compressor which compresses the refrigerant compressed by the first compressor; a condenser which condenses the refrigerant compressed by the second compressor; a supercooling heat exchanger including a first flow channel through which a portion of the refrigerant condensed by the condenser passes in order to be cooled, and a second flow channel for heat exchanging heat with the first flow channel; an expansion instrument which expands the refrigerant cooled by the supercooling heat exchanger; a first bypass channel which guides the refrigerant condensed in the condenser to the second flow channel; a supercooling expander installed in the first bypass channel; and a second bypass channel which interconnects the first and second compressors (50, 51) and the second flow channel to allow the refrigerant passing through the second flow channel to be mixed with the refrigerant compressed by the first compressor so as to be compressed in the second compressor; characterized in that the air conditioner further comprises a shell-tube-type evaporator which includes a shell allowing the refrigerant to pass therethrough and a tube disposed within the shell and allowing water to be heat-exchanged with the shell to pass therethrough, which evaporates the refrigerant expanded by the expansion instrument, and which is connected to a location requiring cold water via a water pipe to supply cold water to the location requiring cold water; and an oil recover flow channel that is provided to recover oil of the shell-tube-type evaporator to the first and second compressors (50, 51); wherein the oil recovery flow channel comprises an evaporator connection flow channel connected to the shell-tube-type evaporator, a first compressor connection flow channel connecting the evaporator connection flow channel and the first compressor, and a second compressor connection flow channel connecting the evaporator connection flow channel and the second compressor. a first compressor which compresses a refrigerant; a second compressor which compresses the refrigerant compressed by the first compressor; a condenser which condenses the refrigerant compressed by the second compressor; a supercooling heat exchanger including a first flow channel through which a portion of the refrigerant condensed by the condenser passes in order to be cooled, and a second flow channel for heat exchanging heat with the first flow channel; an expansion instrument which expands the refrigerant cooled by the supercooling heat exchanger; a first bypass channel which guides the refrigerant condensed in the condenser to the second flow channel; a supercooling expander installed in the first bypass channel; and a second bypass channel which interconnects the first and second compressors (50, 51) and the second flow channel to allow the refrigerant passing through the second flow channel to be mixed with the refrigerant compressed by the first compressor so as to be compressed in the second compressor; characterized in that the air conditioner further comprises a shell-tube-type evaporator which includes a shell allowing the refrigerant to pass therethrough and a tube disposed within the shell and allowing water to be heat-exchanged with the shell to pass therethrough, which evaporates the refrigerant expanded by the expansion instrument, and which is connected to a location requiring cold water via a water pipe to supply cold water to the location requiring cold water; and an oil recover flow channel that is provided to recover oil of the shell-tube-type evaporator to the first and second compressors (50, 51); wherein the oil recovery flow channel comprises an evaporator connection flow channel connected to the shell-tube-type evaporator, a first compressor connection flow channel connecting the evaporator connection flow channel and the first compressor, and a second compressor connection flow channel connecting the evaporator connection flow channel and the second compressor.