A double-wall-tube heat exchanger has outer and inner tubes. A clearance between the outer and inner tubes and the interior of the inner tube serve as refrigerant flow paths. Opposite end portions of the inner tube project from opposite ends of the outer tube. The outer tube includes expanded portions formed near the opposite ends. Contracted portions are formed on the outer tube to be located on the outer sides of the expanded portions, and are brazed to the inner tube. Longitudinally extending ridges project radially inward from the inner circumferential surface of the outer tube at predetermined circumferential intervals. The ridges on the inner circumferential surfaces of the expanded portions and the contracted portions are crushed. The clearances between the inner tube and portions of the contracted portions of the outer tube where the ridges are not formed are filled with a brazing filler metal.