Porous film, separator for cell, and cell

A porous thermoplastic resin film capable of functioning well as a separator of a cell is provided. The porous film is constituted with a thermoplastic resin and a filler, wherein X R defined by the following formula: X R = 25 × T GUR × d 2 /Y is smaller than 5, where Y (µm), T GUR (sec/100 cm 3 ), and d (µm) represent the thickness, the gurley value, and the average pore diameter of said film, respectively. The porous film constructed as shown above can reduce the internal resistance of a cell when used as a separator of the cell.