TECHNOLOGY FOCUS - POLYMERS - Preferred Properties: Polymer (II) has a double bond. Polymer (III) carries out chemical bonding to the pore inner surface of the base material.Preferred Polymer: Polymer (I) is ultra high molecular weight polyethylene with weight average molecular weight of 500000 or more.Preferred Composition: The resin composition further contains 1 or more types of thermoplastic elastomer chosen from polystyrene group, polyolefin type and polyester type elastomer.Preferred Method: The pores of the porous base material is further filled with polymer (IV) having proton conductivity. EXAMPLE - A polymer composition (in wt.pts) (15) containing Norsorex NB (RTM: open ring polymer of norbornene with weight average molecular weight of 2 million or more) (2 wt.%), TPE821 (RTM: thermoplastic elastomer with softening point of 109degreesC) (16 wt.%) and ultra high molecular weight polyethylene (weight average molecular weight of 2 million) (81 wt.%) was mixed with liquid paraffin (85) at 160degreesC for 60 minutes. The kneaded material was quenched to sheet-type resin. The sheet type resin was heat pressed and bi-axially stretched to obtain fine porous film-form base material. The base material was heat processed at 85degreesC for 2 hours and at 116degreesC for 2 hours and cross-linked to obtain cross-linked porous film base material. The thickness, porosity, contraction-stress ratio of machine direction and intersection direction of the porous base material was 21 microns, 45% and 1, respectively. 2-acrylamide-2-methyl propane sulfonic acid (99 mol%) and methylene bis acrylamide (1 mol%) were mixed with water to obtain an aqueous solution of 50 wt.% concentration. The solution was mixed with water-soluble azo-type initiator (1 mol%). The porous base material was immersed in the obtained liquid, irradiated with visible light for 6 hours and heated at 50degreesC for 18 hours. Excess polymer was removed from the surface of the film, ion exchange was carried out, water washed and dried to obtain electrolyte film. The proton conductivity along machine direction, proton conductivity along intersection direction and average proton conductivity of the obtained film was 0.058 S/cm, 0.054 S/cm and 0.056 S/cm, respectively.