An artificial lung is provided that includes a plurality of porous hollow fiber membranes for gas exchange comprising a hydrophobic polymer material, wherein the hollow fiber membranes have inner surfaces forming lumens and outer surfaces, and wherein at least one of the inner surfaces or the outer surfaces is coated with a polymer-containing solution that has a surface tension of 40 to 55 dyn/cm and that contains a solvent and a polymer having a structural unit represented by Formula (I): wherein in Formula (I), R3 represents a hydrogen atom or a methyl group, R1 represents an alkylene group having 1 to 4 carbon atoms, and R2 represents an alkyl group having 1 to 4 carbon atoms.