Provided is an air conditioner including a connection pipe connected to a refrigerant pipe disposed inside an outdoor heat exchanger that operates as a condenser during a cooling operation and as an evaporator during a heating operation, a header connected to the connection pipe, wherein a refrigerant separated from a two-phase refrigerant flowing through the refrigerant pipe flows through the header, a bypass pipe connected to the header to guide a flow of the refrigerant to a compressor, a flow rate control valve installed at the bypass pipe to control a flow velocity of the refrigerant, a subcooler configured to superheat the refrigerant flowing through the bypass pipe, and a controller configured to control an opening degree of the flow rate control valve.