A heat exchanger includes a duct, a stacked core, and a coupling plate. The duct includes a first plate that is disposed to face at least one of end faces of the stacked core in a core width direction, and a second plate that is disposed to face at least one of the end faces of the stacked core in a tube stacking direction. The second plate includes a second-plate end plate portion disposed to face the end face of the stacked core in the core width direction and brazed to a wall surface of the first plate, a second-plate center plate portion that is disposed to face the end face of the stacked core in the tube stacking direction, and a flange portion that extends in the tube stacking direction and is brazed to a bottom wall surface of a groove portion of the coupling plate.