An upper header tank of an evaporator is formed by three plates. The outside plate has an inflow-side refrigerant-passage outwardly bulging portion whose one end portion communicates with a refrigerant inlet. The inside plate has tube insertion holes. The intermediate plate has communication holes for establishing communication between the tube insertion holes of the inside plate and the outwardly bulging portion of the outside plate. The communication holes of the intermediate plate are connected by communication portions so as to form a resin passage communicating with the outwardly bulging portion. Of all the communication portions of the refrigerant passage, a plurality of upstream communication portions are smaller in width than the remaining communication portions. The relation 0.25.ltoreq.A/B.ltoreq.0.35 is satisfied, where A represents the number of the narrow communication portions, and B represents the total number of the communication holes which form the refrigerant passage.