An artificial lung is provided having a plurality of porous hollow fiber membranes for gas exchange, in which the hollow fiber membranes have outer surfaces, inner surfaces forming lumens, and opening portions through which the outer surfaces communicate with the inner surfaces, any one of the outer surfaces and the inner surfaces is coated with a colloidal solution of an antithrombotic material containing a polymer as a main component, and an average particle size of the colloid is at least 1.5 times a diameter of the opening portions of the hollow fiber membranes. An artificial lung is provided that can effectively suppress leakage of blood plasma components after blood circulation (blood plasma leakage).