An air conditioner comprising: a compressor for compressing refrigerant; an outdoor heat exchanger installed in an outdoor space for performing heat exchange between the refrigerant and outdoor air; an indoor heat exchanger installed in an indoor space for performing heat exchange between the refrigerant and indoor air; a switching valve for guiding the refrigerant, discharged from the compressor, to the outdoor heat exchanger during a cooling operation and to the indoor heat exchanger during a heating operation; and an injection module for injecting a portion of the refrigerant, discharged from the indoor heat exchanger, to the compressor, wherein the injection module is configured to perform heat exchange between the portion of the refrigerant discharged from the indoor heat exchanger and refrigerant, which moves from the outdoor heat exchanger to the indoor heat exchanger, during the cooling operation, and injects the heat-exchanged refrigerant into the compressor, wherein the injection module includes: an injection heat exchanger for performing heat exchange between the refrigerant discharged from the indoor heat exchanger and the refrigerant, which moves from the outdoor heat exchanger to the indoor heat exchanger, during the cooling operation; and a first injection expansion valve for expanding refrigerant, which moves between the injection heat exchanger and the compressor, characterized in that the injection module further includes: a cooling bypass pipe for diverting the refrigerant discharged from the indoor heat exchanger to the injection heat exchanger during the cooling operation; and a check valve located in the cooling bypass pipe for preventing the refrigerant from moving from the injection heat exchanger to the indoor heat exchanger during the heating operation. a compressor for compressing refrigerant; an outdoor heat exchanger installed in an outdoor space for performing heat exchange between the refrigerant and outdoor air; an indoor heat exchanger installed in an indoor space for performing heat exchange between the refrigerant and indoor air; a switching valve for guiding the refrigerant, discharged from the compressor, to the outdoor heat exchanger during a cooling operation and to the indoor heat exchanger during a heating operation; and an injection module for injecting a portion of the refrigerant, discharged from the indoor heat exchanger, to the compressor, wherein the injection module is configured to perform heat exchange between the portion of the refrigerant discharged from the indoor heat exchanger and refrigerant, which moves from the outdoor heat exchanger to the indoor heat exchanger, during the cooling operation, and injects the heat-exchanged refrigerant into the compressor, wherein the injection module includes: an injection heat exchanger for performing heat exchange between the refrigerant discharged from the indoor heat exchanger and the refrigerant, which moves from the outdoor heat exchanger to the indoor heat exchanger, during the cooling operation; and a first injection expansion valve for expanding refrigerant, which moves between the injection heat exchanger and the compressor, an injection heat exchanger for performing heat exchange between the refrigerant discharged from the indoor heat exchanger and the refrigerant, which moves from the outdoor heat exchanger to the indoor heat exchanger, during the cooling operation; and a first injection expansion valve for expanding refrigerant, which moves between the injection heat exchanger and the compressor, characterized in that the injection module further includes: a cooling bypass pipe for diverting the refrigerant discharged from the indoor heat exchanger to the injection heat exchanger during the cooling operation; and a check valve located in the cooling bypass pipe for preventing the refrigerant from moving from the injection heat exchanger to the indoor heat exchanger during the heating operation. a cooling bypass pipe for diverting the refrigerant discharged from the indoor heat exchanger to the injection heat exchanger during the cooling operation; and a check valve located in the cooling bypass pipe for preventing the refrigerant from moving from the injection heat exchanger to the indoor heat exchanger during the heating operation.