A heat exchanger including a plurality of horizontally arranged tubes, headers to support the tubes and to enable a refrigerant to flow in the tubes, and a corrugated fin horizontally disposed between the tubes, wherein the corrugated fins includes a vertical fin body, flat contact parts formed at an upper part and a lower part of the fin body, the flat contact parts being in surface contact with a top and a bottom of the tubes, and curved contact parts extending from opposite ends of the flat contact parts, the curved contact parts being in surface contact with the sides of the tubes, the fin body includes drainage guides formed outside the flat contact parts in a lateral direction, and each drainage guide includes protruding parts protruding more upward and downward than the flat contact parts.