A heat exchanger comprising: a tube panel module elongated in an up-down direction and including a plurality of first tube panels and second tube panels that are alternately arranged in a left-right direction; header panel modules respectively formed at an upper end and a lower end of the tube panel module and elongated in a left-right direction; and a header case having an open one side, providing a space therein, and covered on the one side by the cover module such that the first tube panels and the second tube panels communicate with the space, wherein the first tube panel is formed by bonding a first panel and a second panel, the second tube panel is formed by bonding a third panel and a fourth panel, and the header panel module includes: a first header panel formed by bending both ends of the first panel and the second panel in opposite directions; and a second header panel formed by bending both ends of the third panel and the fourth panel in opposite directions and bonded to the first header panel between every first tube panel and second tube panel, wherein the plurality of first header panels are disposed in the same plane, the plurality of second header panels are disposed in the same plane and are bonded to the tops of the first header panels, characterised in that the plurality of second header panels are located above the first header panels, wherein the first header panel and the second header panel are alternately disposed and overlap each other between the first tube panel and the second tube panel. a tube panel module elongated in an up-down direction and including a plurality of first tube panels and second tube panels that are alternately arranged in a left-right direction; header panel modules respectively formed at an upper end and a lower end of the tube panel module and elongated in a left-right direction; and a header case having an open one side, providing a space therein, and covered on the one side by the cover module such that the first tube panels and the second tube panels communicate with the space, wherein the first tube panel is formed by bonding a first panel and a second panel, the second tube panel is formed by bonding a third panel and a fourth panel, and the header panel module includes: a first header panel formed by bending both ends of the first panel and the second panel in opposite directions; and a second header panel formed by bending both ends of the third panel and the fourth panel in opposite directions and bonded to the first header panel between every first tube panel and second tube panel, wherein the plurality of first header panels are disposed in the same plane, the plurality of second header panels are disposed in the same plane and are bonded to the tops of the first header panels, characterised in that the plurality of second header panels are located above the first header panels, wherein the first header panel and the second header panel are alternately disposed and overlap each other between the first tube panel and the second tube panel. a first header panel formed by bending both ends of the first panel and the second panel in opposite directions; and a second header panel formed by bending both ends of the third panel and the fourth panel in opposite directions and bonded to the first header panel between every first tube panel and second tube panel, wherein the plurality of first header panels are disposed in the same plane, the plurality of second header panels are disposed in the same plane and are bonded to the tops of the first header panels, characterised in that the plurality of second header panels are located above the first header panels, wherein the first header panel and the second header panel are alternately disposed and overlap each other between the first tube panel and the second tube panel.