Abstract: An automotive heat exchanger of the parallel flow type includes a number of flat tubes (4), a number of corrugated fins (5), with the flat tubes and the corrugated fins being stacked alternately, the first cylindrical header tank (2) to which the tubes are connected by inserting one end thereof laterally into the first header tank, and the second cylindrical header tank (3) to which the tubes are connected by inserting the other end thereof laterally into the second header tank. The ends of each tube inserted laterally into the header tanks are cut off along the inner peripheral surfaces of the header tanks, thus minimizing the obstruction of flow in the headers. The header tanks may be made substantially elliptical.