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.