Provided are rectangular plate-like fins 2 layered at intervals; and flat tubes 3 which are perpendicularly extended through the layered plate-like fins 2 and are provided on multiple levels along a longitudinal direction of the plate-like fins 2. The plate-like fins 2 are provided with at least one heat transfer promoting section 6 that is positioned in a region between adjacently-positioned flat tubes 3 and in which ridge sections 4 and valley sections 5 having ridgelines extending in the longitudinal direction of the plate-like fins 2 are arranged to alternate. In the heat transfer promoting section 6, at least one slit 7 allowing communication between a front and a back of the plate-like fin 2 is formed on a downwind side of the ridge sections 4.