The purpose of the present invention is to provide a porous membrane that has both high water permeability and excellent protein fractionation performance. Provided is a method for producing a porous membrane, said method comprising a step for discharging a membrane-forming dope that contains a hydrophilic polymer from a slit formed in a mouthpiece, and a step for, after the passage of the discharged membrane-forming dope through a dry part, solidifying the membrane-forming dope in a coagulation bath to give a porous membrane, wherein the cross-section area of the slit is 3-30 times inclusive as large as the cross-section area of the solidified porous membrane.
