The present invention relates to a porous membrane containing cellulose fibers, wherein the cellulose fibers contain 5% by weight or more of cellulose fibers with a diameter of 1 μm or more, relative to the total weight of the cellulose, and the porous membrane has a tensile strength of 50 N·m/g or more, and/or has a tear strength of 0.40 kN/m or more. The porous membrane according to the present invention can provide a separator for electrochemical devices with superior properties, at a reasonable cost.