An air conditioner, comprising: a compressor for compressing a refrigerant; an outdoor heat exchanger, disposed at an outdoor space, for heat-exchanging outdoor air with the refrigerant; an indoor heat exchanger, disposed at an indoor space, for heat-exchanging indoor air with the refrigerant; a valve configured to guide the refrigerant discharged from the compressor to the indoor heat exchanger when performing a heating operation and for guiding the refrigerant discharged from the compressor to the outdoor heat exchanger when performing a defrosting operation; a first injection module including a first injection expansion valve for expanding a first portion of the refrigerant, and a first injection heat exchanger for heat-exchanging a second portion of the refrigerant with the first portion of the refrigerant expanded at the first injection expansion valve for supercooling the heat-exchanged refrigerant; a second injection module including a second injection expansion valve for expanding a first portion of the refrigerant, and a second injection heat exchanger for heat-exchanging a second portion of refrigerant with the first portion of the refrigerant expanded at the second injection expansion valve for supercooling the heat-exchanged refrigerant; wherein the air conditioner is configured such that the first injection module injects the refrigerant into a high pressure side of the compressor; and the second injection module injects the refrigerant into a low pressure side of the compressor; a controller configured to control the air conditioner; wherein the controller is configured to control the first injection module and the second injection module such that the first injection module injects a portion of the refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor when performing the heating operation and does not inject a portion of the refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor when performing the defrosting operation; and the second injection module injects a portion of the refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor when performing the heating operation and injects a portion of the refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor when performing the defrosting operation, such that the second injection module does not inject the refrigerant into the compressor, when an injection superheat, that is, a difference between a temperature of the refrigerant injected into the compressor and a temperature of the refrigerant expanded at the second injection expansion valve is higher than a predetermined reference injection superheat, when performing the defrosting operation. a compressor for compressing a refrigerant; an outdoor heat exchanger, disposed at an outdoor space, for heat-exchanging outdoor air with the refrigerant; an indoor heat exchanger, disposed at an indoor space, for heat-exchanging indoor air with the refrigerant; a valve configured to guide the refrigerant discharged from the compressor to the indoor heat exchanger when performing a heating operation and for guiding the refrigerant discharged from the compressor to the outdoor heat exchanger when performing a defrosting operation; a first injection module including a first injection expansion valve for expanding a first portion of the refrigerant, and a first injection heat exchanger for heat-exchanging a second portion of the refrigerant with the first portion of the refrigerant expanded at the first injection expansion valve for supercooling the heat-exchanged refrigerant; a second injection module including a second injection expansion valve for expanding a first portion of the refrigerant, and a second injection heat exchanger for heat-exchanging a second portion of refrigerant with the first portion of the refrigerant expanded at the second injection expansion valve for supercooling the heat-exchanged refrigerant; wherein the air conditioner is configured such that the first injection module injects the refrigerant into a high pressure side of the compressor; and the second injection module injects the refrigerant into a low pressure side of the compressor; a controller configured to control the air conditioner; wherein the controller is configured to control the first injection module and the second injection module such that the first injection module injects a portion of the refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor when performing the heating operation and does not inject a portion of the refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor when performing the defrosting operation; and the second injection module injects a portion of the refrigerant flowing from the indoor heat exchanger to the outdoor heat exchanger into the compressor when performing the heating operation and injects a portion of the refrigerant flowing from the outdoor heat exchanger to the indoor heat exchanger into the compressor when performing the defrosting operation, such that the second injection module does not inject the refrigerant into the compressor, when an injection superheat, that is, a difference between a temperature of the refrigerant injected into the compressor and a temperature of the refrigerant expanded at the second injection expansion valve is higher than a predetermined reference injection superheat, when performing the defrosting operation.