To raise the heat conductive coefficient of a boundary film on the side of fluid to be cooled, by letting cooling water flow dawn to the heat conductive wall face of an orthogonal passage whose top and bottom are open, and circulating this while evaporating this by the contact with atmospheric air for cooling, and cooling the fluid flowing in the spiral passage whose top and bottom are closed.

Cooling water is pressure-sent from a lower tank 6 by a circulation pump 7, and it is sprayed equally from the topside of an orthogonal passage 1B spiral in cross section by means of a rotary sprinkling pipe 8 at the top, and it wets a spiral heat conductive board, and flows down while cooling the cooling fluid for cooling flowing the spiral passage from the periphery to the center. The air to cool this enters the orthogonal passage 1B, being taken in from the louver 5 arranged at the lower side face, and evaporates and cools this while going up, becoming an opposite flow to the cooling water flowing down. Accordingly, for the heat conductive coefficient of the boundary film, a higher numerical value can be obtained, as compared with the case where it flows in a coil pipe.