An artificial lung includes a housing, a tubular hollow fiber membrane bundle contained in the housing and providing a multiplicity of hollow fiber membranes having a gas exchange function, a gas inflow port and a gas outflow port communicating with each other through hollow portions of the hollow fiber membranes, and a blood inflow port and a blood outflow port through which blood is distributed. The tubular hollow fiber membrane bundle has a cylindrical overall shape, and a filter member having a bubble-trapping function is provided on an outer peripheral portion of the tubular hollow fiber membrane bundle.