Provided is a separator which can make the electric field on the surface of a negative electrode for a metal secondary battery homogeneous to thereby prevent the formation of dendrites. A porous separator for metal secondary batteries, which has a polymer electrolyte layer formed on the surface layer of at least one main surface of a porous polyimide film. It is preferred that the polymer electrolyte layer is composed of both a polymer electrolyte material which is supported on at least one main surface of the porous polyimide film and a polymer electrolyte material which is supported in voids in a layered region that extends from the main surface.