A heat exchanger (10) has a clad thin sheet material (2), a clad thick sheet material (1) that is disposed so as to define a passage (4) between the clad thick sheet material (1) and the clad thin sheet material (2), and that has a sheet thickness greater than that of the clad thin sheet material (2), and an inner fin (3) held between the clad materials (1, 2). The clad thick sheet material (1) and the clad thin sheet material (2) have Zn-containing brazing filler metal layers (12, 22) on their passage (4) sides, respectively, and the post-brazing surface Zn amounts A1 and A2 are set so as to satisfy specific conditions. Further, certain conditions concerning the compositions of each of the layers that constituting the clad materials (1, 2), and the inner fin (3) are set.