PURPOSE: To prevent a short circuit due to fragments of a drop from occurring, by forming a polyolefin resin porous film in both upper and lower parts of a separator using a polyamide fabric or a nonwoven fabric.

CONSTITUTION: Both upper and lower parts in the longitudinal direction of a polyamide fabric or a nonwoven fabric constituting a separator 2 are made up of each polyolefin resin porous film 1. For example, after a film 1 composed of 6-nylon web and polyethylene is impregnated in an aqueous solution of polyvinyl alcohol, the film 1 composed of polyethylene is sandwiched with the 6-nylon web and dried up. This film is pressed with a heated roll and the separator 2 of the nonwoven fabric is produced. With this constitution, not only weight per unit area increases but also a perfect network structure is secured, while such an inorganic substance as fine silicic acid is mixed in the film so that penetration in the separator due to fragments of a drop is reduced, thus a short circuit is preventable from occurring.