A heat exchanger is formed by the stacked lamination of a plurality of core elements formed from a single material. The core elements are substantially U-shaped with an upper surface having fins for allowing a first heat medium to pass therethrough, side plates extending substantially perpendicular to the ends of the upper surface for joining adjacent core elements, and tube portions formed between the side plates of joined adjacent core elements. The core elements are stacked and joined to thereby form a finned passageway allowing a first heat medium to pass therethrough in a first direction, and a tube passageway allowing a second heat medium to pass therethrough in a second direction which is perpendicular to the first direction. The design allows for adjustment of the cross-sectional area of the tube passageway without causing an increase in the pressure caused by the finned passageway.