A heat exchanger in which a connecting part may be coupled to a header tank of the heat exchanger in the short term without using a separate coupling component before a brazing process is performed, and a coupling method of a connecting part thereof. The connecting part is coupled to a first header tank or a second header tank while surrounding a predetermined region of an outer peripheral surface of the first header tank or the second header tank, a region of the connecting part to which external force is locally applied being coupled to the first header tank or the second header tank while protruding together with the first header tank or the second header tank.