Porous membrane, process for producing porous membrane, process for producing clarified liquid, and porous-membrane module

A porous hollow fiber membrane whose membrane wall is constructed of a hydrophobic polymer and a hydrophilic polymer,

• wherein when the membrane wall has a total film thickness and is divided into 3 sections in the film thickness direction to form region “a” containing an outer wall surface A of the hollow fiber membrane wall, region “c” containing an inner wall surface C and region “b” between region “a” and region “c”,
• the hydrophilic polymer content ratio Ca in region “a”, the hydrophilic polymer content ratio Cb in a region “b” and the hydrophilic polymer content ratio Cc in region “c” satisfy the following inequality (I) and inequality (III):
• Ca>Cb>Cc (I), and
• Ca/Cc≧2 (III)
• the mean pore size of the inner wall surface C is larger than the mean pore size of the outer wall surface A,
• wherein the thickness of each of the regions “a”, “b”, and “c” in the range of 33%±5% of the total film thickness, and
• wherein the hydrophilic polymer comprises polyvinylpyrrolidone with a weight-average molecular weight of between 20,000 and 1,000,000.