The fin-tube heat exchanger includes a group of fins arranged parallel to one another at predetermined intervals; cylindrical fin collars formed on each fin at a predetermined column pitch and a predetermined row pitch; and heat transfer tubes extending through the respective fin collars and secured thereto in intimate contact therewith. Seat portions are formed on each fin around the fin collars. A curved protuberance of a generally angular cross-section is formed on the fin adjacent to an outer periphery of each of the seat portions, which has a ridge line of an arcuate or circular shape arranged in concentric relation to the associated fin collar. A plurality of straight protuberances of a generally angular cross-section are formed on each fin adjacent to outer peripheries of the respective seat portions between any two adjacent rows of the fin collars. With this structure, heat transfer performance is improved by a turbulence promoting effect of the straight protuberances. Also an air flow is guided into slip streams behind the heat transfer tubes by the curved protuberances, thereby reducing stagnation zones and increasing the effectively used heat transfer area to improve heat transfer performance.
