There is provided a heat exchanger 10 in which each of header tanks 20A and 20B is configured so that each of intermediate plates 60 and 90 is held between a header plate 40 and a tank plate 50. The intermediate plate 60, 90 functions as a reinforcing member, so that the strength of the header tank 20A, 20B is improved. The intermediate plate 60, 90 serving as a reinforcing element comprises bent parts 100 between the central portion and both the end portions in the width direction of the header tank 20A, 20B. By the elastic deformation of the bent parts 100, for example, the stresses developed in brazing of the header tank 20A, 20B, and the stresses at the time when a refrigerant pressure is applied can be prevented from concentrating in the joint portion of the header plate 40, the tank plate 50, and the intermediate plate 60, 90.