To eliminate temperature rise of engine cooling water through direct air cooling system by provided end caps being bonded to the opposite ends of a housing containing a heat exchanging metal honeycomb structure rotatably with high temperature fluid inlet and outlet and low temperature fluid inlet and outlet, respectively.

A tubular housing 1 for containing a metal honeycomb structure 2 is fixed, to the opposite ends thereof, with end caps 3a, 3b for providing low temperature fluid inlet 4-1, a high temperature fluid outlet 5-2 and low temperature fluid outlet 4-2 and high temperature fluid inlet 5-1. Outer end part of a shaft 9 touching rod-like seals 6 being fixed to the opposite ends of a tubular case 2-4 penetrates the end cap 3a rotatably through a bearing 10 while being supported and the shaft is driven by means of a motor or an engine through a pulley 11 or a belt secured to the shaft end. Alternatively, the shaft can be driven by providing a pulley on the outer circumference of the metal honeycomb structure 2 as other rotary drive means.