A membrane artificial lung performs gas exchange between blood and a gas via the membrane by flowing the blood in one side of the membrane and flowing oxygen or an oxygen-containing gas in the other side of the membrane. The membrane has a hollow fiber membrane of poly-4-methylpentene-1 and an oxygen permeation rate Q(O₂) at 25 C. of from 110^-6 to 310^-3 (cm³(STP)/cm²seccmHg) and an ethanol flux of from 0.1 to 100 ml/minm². The membrane has, in the side of the blood flow, a surface having an ionic complex derived from: quaternary aliphatic alkylammonium salts; and heparin or a heparin derivative. The quaternary alkylammonium salts are a quaternary aliphatic alkylammonium salt having from 22 to 26 carbon atoms in total and a quaternary aliphatic alkylammonium salt having from 37 to 40 carbon atoms in total.