A heat exchanger includes a shell and a plurality of tubes. The shell includes a heat exchange region in which a second refrigerant is to be introduced into the shell, so that a heat exchange occurs between the second refrigerant and a first refrigerant which flows through the plurality of tubes. The shell includes an inlet region through which the first refrigerant is introduced into the shell, a reverse region into which the first refrigerant is introduced, after the first refrigerant passes through the heat exchange region, and an outlet region into which the first refrigerant is introduced, after the first refrigerant passes through the reverse region and the heat exchange region, the first refrigerant being discharged out of the shell from the outlet region. The shell includes partition plates to divide the heat exchange region, the inlet region, the reverse region, and the outlet region.