A plate type heat exchanger arranged so that heat exchange is effected between fluids through heat transfer plates. It comprises heat transfer plates serving as heat transfer elements, and jet plates each having a number of small holes. One fluid is jetted through the small holes in the jet plates towards the heat transfer plates opposed to the jet plates while the other fluid flows along the respective opposite heat transfer surfaces of the heat-transfer plates or is jetted toward the respective opposite heat transfer surfaces as in the case of the first fluid.