An air conditioner comprising: a compressor for compressing a refrigerant; an oil separator for separating an oil of the refrigerant discharged from the compressor to collect the separated oil into the compressor ; a condenser for condensing the refrigerant separated from the oil separator ; and a supercooling part in which a main refrigerant that is the refrigerant condensed by the condenser is heat-exchanged with a branch refrigerant branched from the main refrigerant, and an injection passage through which the branch refrigerant flows and configured to inject refrigerant passing through the supercooling part into the compressor ; an injection expansion valve disposed in the injection passage ; an injection introduction part disposed in the compressor , the injection introduction part being connected to the injection passage , an oil collection passage for collecting the oil separated by the oil separator into the compressor , a first oil injection passage connecting one position of the oil collection passage to the supercooling part to guide the oil into the supercooling part , a second oil injection passage connected to the first oil injection passage to discharge the oil cooled in the supercooling part , wherein the injection passage connects the supercooling part to the injection introduction part of the compressor , characterized in that the air conditioner further comprises: that the second oil injection passage is connected to a combination part of the injection passage , a control device for controlling the operation of the air conditioner ; wherein when a heating load is less than a predetermined load, the control device is configured to close the injection expansion valve , such that at least a portion of the oil in the oil separator passes through the supercooling part , and is heat-exchanged with the main refrigerant in the supercooling part , and is introduced into the compressor through the injection passage . a compressor for compressing a refrigerant; an oil separator for separating an oil of the refrigerant discharged from the compressor to collect the separated oil into the compressor ; a condenser for condensing the refrigerant separated from the oil separator ; and a supercooling part in which a main refrigerant that is the refrigerant condensed by the condenser is heat-exchanged with a branch refrigerant branched from the main refrigerant, and an injection passage through which the branch refrigerant flows and configured to inject refrigerant passing through the supercooling part into the compressor ; an injection expansion valve disposed in the injection passage ; an injection introduction part disposed in the compressor , the injection introduction part being connected to the injection passage , an oil collection passage for collecting the oil separated by the oil separator into the compressor , a first oil injection passage connecting one position of the oil collection passage to the supercooling part to guide the oil into the supercooling part , a second oil injection passage connected to the first oil injection passage to discharge the oil cooled in the supercooling part , wherein the injection passage connects the supercooling part to the injection introduction part of the compressor , that the second oil injection passage is connected to a combination part of the injection passage , a control device for controlling the operation of the air conditioner ; wherein when a heating load is less than a predetermined load, the control device is configured to close the injection expansion valve , such that at least a portion of the oil in the oil separator passes through the supercooling part , and is heat-exchanged with the main refrigerant in the supercooling part , and is introduced into the compressor through the injection passage . <EOS>