The present heat exchanger (A) comprises a thermal element (1), one side of which becomes cold and the other side becomes hot once energized with electricity, a high heat-conductive intermediate plate (2) in contact with one surface of this element (1); a high heat-conductive porous material (3) in contact with the other surface of the intermediate plate (2); and an upper plate (4) provided on the other side of this material (3). Once the thermal element (1) is activated in the heat exchanger (A), the intermediate plate (2) and the porous material (3) are rapidly cooled or heated. Meanwhile, since the temperature of fluid passing through within the porous material (3) is different than the temperature of the material itself (3), heat exchange is ensured between the fluid and the porous material.