A heat exchanger is provided in which second heat transfer plates (42) and first heat transfer plates (not illustrated) are alternately superimposed so as to form high pressure fluid passages (63) and low pressure fluid passages (not illustrated). The high pressure fluid passages (63) include inlet fluid passages (65a, 65b) defined by inlet ridges (50a to 50c) extending from a compressed air inlet (19), and main fluid passages (64) defined by a plurality of main ridges (49) extending parallel to each other in the longitudinal direction of the second heat transfer plates (42) so as to be perpendicular to the inlet fluid passages (65a, 65b). The two inlet fluid passages (65a, 65b) have different widths (Wa, Wb), and gaps (, ) are formed between the downstream ends of the two inlet ridges (50b, 50c) and the upstream ends of the main ridges (49). A high pressure fluid can thereby be uniformly distributed into the main fluid passages (64) connected to the inlet fluid passages (65a, 65b) of the high pressure fluid passages (63) of the heat exchanger.