A heat exchanger is provided that includes a tube panel module elongated in a vertical direction and including a plurality of first tube panels and a plurality of second tube panels that are alternately arranged in a lateral direction; header panel modules respectively formed at an upper end and a lower end of the tube panel module and elongated in the lateral direction; and a header case having an open one side, providing a space therein, and covered on the one side by the header panel module such that the plurality of first tube panels and the plurality of second tube panels communicate with the space. Each first tube panel is formed by bonding a first panel and a second panel, and each second tube panel is formed by bonding a third panel and a fourth panel. The header panel modules include 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.