A porous membrane with the membrane wall constructed of a hydrophobic polymer and a hydrophilic polymer, wherein when the membrane wall is divided into 3 sections in the film thickness direction to form region “a” containing one wall surface A of the membrane wall, region “c” containing the other wall surface C and region “b” between region “a” and region “c”, the hydrophilic polymer content ratio Ca in region “a” is greater than the hydrophilic polymer content ratio Cc in region “c”, and the mean pore size of the wall surface C is larger than the mean pore size of the wall surface A.