To solve the problem that it is difficult to enhance heat transfer performance more than in the present state by using a foamed metal having a predetermined condition, whereas it has a limit from the point of productivity that a slit or louver is added to a thin aluminum plate or the like to improve the heat transfer performance regardless of the shape of a heat transfer fin to be applied.

This heat transfer fin for air heat exchanger comprises heat transfer pipes 1 and 1 for carrying a fluid to be heat-exchanged with air; and heat transfer fins 13 and 13 which make contact with air to exchange heat, the heat transfer fins 13 and 13 being composed of a foamed metal. The foamed metal has a pore density of 20 PPI or more. According to this, the heat transfer performance can be significantly improved.