A communication chamber communicated with the downstream end of a condensing part is provided within a header. A gas-liquid separation chamber is provided beside the communication chamber for separating the refrigerant into gas and liquid phases. The height of this gas-liquid separation chamber is set to be smaller than that of the communication chamber to prevent the interference of the gas-liquid separation chamber with peripheral devices of a vehicle to facilitate the installation of the condenser. Further, a refrigerant introducing means is provided at a portion corresponding to a liquid refrigerant pool part at the lower part of the gas-liquid separation chamber within the partition part for introducing the refrigerant within the communication chamber into the liquid refrigerant within the gas-liquid separation chamber.