An air conditioner is provided. The air conditioner may include a supercooling heat exchanger that evaporates a refrigerant, a compressor that compresses the refrigerant, an injection flow channel through which the evaporated refrigerant flows into the compressor, an injection valve that opens and closes the injection flow channel, an oil separator that separates oil from refrigerant discharged from the compressor, and an oil injection line, which communicates at a first end thereof with the oil separator and at a second end thereof with the injection flow channel so as to guide the oil separated by the oil separator toward the injection flow channel. The oil separated by the oil separator may selectively flow into the compressor through the oil injection line and the injection flow channel in accordance with a mode of operation of the air conditioner.