An evaporator has a header tank including a header forming plate with outward bulging portions, a tube connecting plate, and an intermediate plate. Tube insertion holes are formed in the tube connecting plate. Communication holes formed in the intermediate plate cause the tube insertion holes to communicate with the interior of the corresponding outward bulging portion therethrough. At least one of the outward bulging portions allows a refrigerant to flow therethrough longitudinally. All the communication holes in communication with the refrigerant passing bulging portion are held in communication by communication portions for the communication holes, the communication portions providing a refrigerant passageway. The refrigerant passageway is altered in cross sectional area along the longitudinal direction thereof by adjusting the width of the communication portions.