A heat exchanger comprises outer fins; a plurality of tubes arranged alternately with the outer fins; and header tanks receiving open ends of the tubes for communication with the tubes. The header tanks each comprise a first member and a second member which are combined to each other. The first member has tube insertion slots into which the open ends of the tubes are inserted, the second member does not have the tube insertion slots. The first member is either a core material having no brazing material layers on outer and inner peripheral surfaces thereof, or a core material having a brazing material layer on an outer peripheral surface thereof but having no brazing material layer on an inner peripheral surface thereof. The second member is brazed to the outer or inner peripheral surface of the first member having no brazing material layer thereon.