To manufacture a solid electrolyte having a sufficient impregnation quantity at a high impregnating speed and a relatively low temperature by impregnating a resin molded body mainly composed of a polymer, such as polyacrylonitrile with a specified quantity of aprotic polar organic solvent as the solvent for electrolyte.

An aprotic polar organic solvent having a high boiling point such as ethylenecarbonate which is usable as the solvent for electrolyte, or a mixture thereof is included in a resin molded body mainly composed of at least one of polyacrylonitrile, polyoxymethylene, polyvinylidene fluoride, polyacrylate, and copolymers mainly composed of them by means of impregnation to provide a polymer solid electrolyte precursor. An electrolytic solution or electrolyte is brought into contact with a precursor to diffuse the electrolyte, whereby a polymer solid electrolyte is provided. In the actual manufacture of a secondary battery, it is sufficient that this precursor and an electrolyte are laminated with the electrolyte which is imparted to either one thereof, or both are laminated and then dipped in the electrolytic solution.