A corrugated fin comprises a first part which is interposed between paired first tubes, a second part which is interposed between paired second tubes and a third part through which the first and second parts are integrally connected. The third part of the corrugated fin is formed with louvers which extend in a direction perpendicular to upper and lower folded edge portions of the first and second parts. Each of the louvers is of a half-louver type including an elongate flat portion which is bent up or down along a lower edge thereof from a major portion of the third part and two generally triangular supporting portions which support longitudinal ends of the elongate flat portion from the major portion.