Abstract: A recess portion for setting an attachment position is formed in each plate fin at positions adjacent to both longitudinal ends of the plate fins on both upstream and downstream ends in an air flowing direction. Therefore, air passing through the plate fins is disturbed by a standing wall portion of the recess portion around the longitudinal ends of the plate fins. Thus, it can prevent a thermal boundary layer from being expanded in a heat exchanger having the plate fin, and heat-transmission efficiency can be improved in the heat exchanger. As a result, an entire area of the plate fin can be effectively used, thereby improving heat-exchanging capacity of the heat exchanger.