This heat exchanger includes a core and a header tank. The entire peripheral edge of an opening of the header tank welded to the core has a bevel inclined from the internal surface of the header tank toward the external surface thereof at a predetermined bevel angle. At least a portion of the peripheral edge of the opening of the header tank has a second inclined portion inclined from the external surface of the header tank toward the internal surface thereof at an angle larger than the predetermined bevel angle.
