A heat exchanger includes a main core portion (6) for conducting heat exchange between an air and a refrigerant, a receiver tank (8) into which the refrigerant having passed through the main core portion flows, and a subcool core portion (10) for supercooling and liquefying a gas-liquid mixed refrigerant having passed through the receiver tank by heat exchange with the air, wherein the subcool core portion is composed of a plurality of tubes (22) arranged along a crosswise direction between left and right header tanks (20) arranged along the crosswise direction, respectively, in a state in parallel with each other and communicating with both the left and right header tanks; and fins (24) arranged between the adjacent tubes.