In a heat exchanger, a core portion includes a plurality of plate fins each shaped like a flat plate and a plurality of tubes in which a fluid flows and each of which is inserted into each of the plate fins to be mechanically bonded thereto. Further, an end portion in a longitudinal direction of each of the tubes is bonded to a header plate which constructs a part of a header tank. The manufacturing method for this heat exchanger includes inserting the tube into the plate fins; expanding the tube to attach the plate fins; connect the tube into the header plate; and vibrate the tube with respect to the plate while applying a load to the tube in the direction of the header plate.