An evaporator including a refrigerant inlet header having a refrigerant inlet at one end thereof, and a plurality of heat exchange tubes arranged at a spacing longitudinally of the inlet header and each having one end joined to the inlet header. The interior of the inlet header is divided by a flow dividing control wall into an upper space for admitting a refrigerant thereinto through the refrigerant inlet and a lower space communicating with the heat exchange tubes. The control wall has a communication hole formed in an end portion thereof opposite to the refrigerant inlet. The upper and lower spaces communicate with each other through the communication hole so that the refrigerant flows through the lower space in a direction opposite to the direction of flow of the refrigerant in the upper space. The evaporator achieves a high heat exchange efficiency.