A heat exchanger includes a plurality of tubes 2 through an inner cavity of which a heat-transfer medium liquid flows, a sealing member 6 that seals the plurality of tubes 2 while exposing both ends thereof, with a blood channel passing outside each of the tubes 2 being formed in a central portion in the axial direction of the tubes, and a housing 5 that accommodates the tubes 2 sealed with the sealing member 6. The heat exchanger further includes a hollow fiber membrane 3 that is formed of a plurality of hydrophobic and gas permeable hollow fibers 4 and that is disposed on at least one of an entrance side and an exit side of the blood channel in the housing 5 so that a liquid flowing through the blood channel passes through the hollow fiber membrane 3. The housing 5 includes openings 10 for exposing open ends of each of the hollow fibers 4 forming the hollow fiber membrane 3 to the outside, and gaps between an inner side of the openings and the hollow fibers 4 are sealed. Air can be removed while suppressing a reduction in the heat exchange efficiency.