Provided is a porous membrane which has a high water permeability performance, a high blocking performance, and a durability performance against loads of long-term and high operation pressures, which are suitable for filtering applications. The porous membrane includes one surface to be on a side of a filtrate; and the other surface to be on a side of a liquid to be filtered, wherein a surface pore diameter index of the one surface is 2.5 or more, the surface pore diameter index being determined by dividing a pore diameter in a top surface by a pore diameter in a second top surface.