A virtual quadrangle having vertexes respectively configured by: inner ends which are located respectively at a corner of inner cut end faces of the louvers formed in flat portions that are opposed to each other across the bent portion; and outer ends which are located respectively at a corner of outer cut end faces of the louvers, is assumed. A distortion adjusting portion is disposed in the bent portion of the louver fin. The distortion adjusting portion equalizes distortion generated in the direction of an inner diagonal line connecting the inner ends of the virtual quadrangle, with that generated in the direction of an outer diagonal line connecting the outer ends of the virtual quadrangle. Thereby, the louver fin can be prevented from being curved in the longitudinal direction.