An oxygenator includes: a housing； a hollow fiber membrane layer that is stored in the housing and has multiple integrated hollow fiber membranes with a gas exchange function； a gas inlet portion and a gas outlet portion that are provided on the upstream and downstream of gas passages in lumens of the hollow fiber membranes, respectively； a blood inlet portion and a blood outlet portion that are provided on the upstream and downstream of blood passages outside the hollow fiber membranes, respectively； a first filter member that is provided on the hollow fiber membrane layer in contact with a blood outlet portion side surface so as to cover substantially the entire surface and has a function to catch bubbles in blood； and a second filter member that is separated from the first filter member, positioned between the first filter member and the blood outlet portion, and has a function to catch bubbles in blood.
