A layered heat exchanger, for example for use for motor vehicle coolers. To provide a turn portion in the heat exchanger for changing flow direction of a fluid flowing zigzag through a fluid circuit, a metal plate is provided at the upper or lower ends of a partition ridge with a fluid flow direction changing passage forming caved portion having a bottom wall of circular-arc cross section. Front and rear upper or lower tank portions are held in communication with each other through a fluid flow direction changing passage of approximately circular cross section and formed by the caved portions opposed to each other. The turn portion is diminished in stress concentrated thereon due to fluid internal pressure and given an increased resistance to pressure to effectively prevent tank side walls from breaking, consequently making it possible to decrease the metal plates thicknesses, to achieve a cost reduction by the decreased thickness and to assure an improved heat exchange efficiency.