An artificial lung 100 has a filling portion 110 that communicates with an inlet port 101 and an outlet port 102 for blood and is filled with blood, a heat exchange portion 160 that includes a bundle of a plurality of hollow fibers 163 for heat exchange and is provided inside the filling portion, a gas exchange portion 170 that includes a bundle of a plurality of hollow fibers 173 for gas exchange and is provided inside the filling portion to be adjacent to the heat exchange portion, and a porous member 180 that is disposed in a gap 190 between the heat exchange portion and the gas exchange portion. A volume within the housing occupied by a wall of the porous member correspondingly reduces a priming volume within the housing available for conveying the blood (i.e., a bulk volume of the porous member partially blocks or fills the gap.
