In a plate laminate type heat exchanger a plurality of groove-like protrusions is formed on one side of each of flat core plates, and the protrusions extend substantially in parallel to one another from one end side in the longitudinal direction of the plate toward the other end side in the longitudinal direction of the plate, form a U-turn region in an area on the other end side in the longitudinal direction of the plate, and return to the one end side in the longitudinal direction of the plate. The plate is curved in such a way that ridges and valleys are formed on part of the plate, the area in which the protrusions are formed but the U-turn region is not formed, in the direction in which the plate is laminated and the ridges and valleys are repeated along the longitudinal direction. Both ends of each of the protrusions converge into an inlet port for high temperature fluid and an outlet port for high temperature fluid, respectively.