A heat exchanger for an air conditioner, the heat exchanger comprising: a plurality of flat heat transfer tubes through which a refrigerant flows; a plurality of fins configured to be arranged on outer surfaces of the plurality of flat heat transfer tubes; first and second headers (40, 50) configured to be disposed on opposite ends of the plurality of flat heat transfer tubes, respectively; at least one baffle (61, 62, 63) configured to be disposed in at least one of the first header or the second header and partition an inner space of the at least one header; and a refrigerant flow control device (100, 200) configured to be disposed on the at least one baffle, allow the refrigerant to selectively pass through the at least one baffle, and control a flow of the refrigerant, wherein the refrigerant flow control device is configured to: block the flow of the refrigerant to prevent the refrigerant from passing through the refrigerant flow control device in a case where the refrigerant flows in one direction in the at least one header, allow the refrigerant to pass through the at least one baffle through the refrigerant flow control device in a case where the refrigerant flows in a direction opposite to the one direction in the at least one header, and control a flow rate of the refrigerant passing through the refrigerant flow control device, the heat exchanger being characterized in that the refrigerant flow control device includes: a communicating pipe disposed on the at least one baffle; and a refrigerant flow rate adjusting member (120, 220) disposed on one end of the communicating pipe, having a hollow cylindrical shape communicating with the communicating pipe, and having a side surface in which refrigerant passages, through which the refrigerant passes, are formed. a plurality of flat heat transfer tubes through which a refrigerant flows; a plurality of fins configured to be arranged on outer surfaces of the plurality of flat heat transfer tubes; first and second headers (40, 50) configured to be disposed on opposite ends of the plurality of flat heat transfer tubes, respectively; at least one baffle (61, 62, 63) configured to be disposed in at least one of the first header or the second header and partition an inner space of the at least one header; and a refrigerant flow control device (100, 200) configured to be disposed on the at least one baffle, allow the refrigerant to selectively pass through the at least one baffle, and control a flow of the refrigerant, wherein the refrigerant flow control device is configured to: block the flow of the refrigerant to prevent the refrigerant from passing through the refrigerant flow control device in a case where the refrigerant flows in one direction in the at least one header, allow the refrigerant to pass through the at least one baffle through the refrigerant flow control device in a case where the refrigerant flows in a direction opposite to the one direction in the at least one header, and control a flow rate of the refrigerant passing through the refrigerant flow control device, the heat exchanger being characterized in that the refrigerant flow control device includes: a communicating pipe disposed on the at least one baffle; and a refrigerant flow rate adjusting member (120, 220) disposed on one end of the communicating pipe, having a hollow cylindrical shape communicating with the communicating pipe, and having a side surface in which refrigerant passages, through which the refrigerant passes, are formed. block the flow of the refrigerant to prevent the refrigerant from passing through the refrigerant flow control device in a case where the refrigerant flows in one direction in the at least one header, allow the refrigerant to pass through the at least one baffle through the refrigerant flow control device in a case where the refrigerant flows in a direction opposite to the one direction in the at least one header, and control a flow rate of the refrigerant passing through the refrigerant flow control device, the heat exchanger being characterized in that the refrigerant flow control device includes: a communicating pipe disposed on the at least one baffle; and a refrigerant flow rate adjusting member (120, 220) disposed on one end of the communicating pipe, having a hollow cylindrical shape communicating with the communicating pipe, and having a side surface in which refrigerant passages, through which the refrigerant passes, are formed. a communicating pipe disposed on the at least one baffle; and a refrigerant flow rate adjusting member (120, 220) disposed on one end of the communicating pipe, having a hollow cylindrical shape communicating with the communicating pipe, and having a side surface in which refrigerant passages, through which the refrigerant passes, are formed.