NOVELTY - A molten salt monomer having quaternary ammonium salt structure comprising quaternary ammonium cation and anion, and polymerizable functional group is graft-polymerized onto polymer (a) having fluorine-containing repeating unit (I), to obtain fluorinated polymer.    USE - Manufacture of fluorinated polymer used in composite polymer electrolyte composition for lithium ion battery or lithium ion capacitor, polymer electrolytic membrane fuel cell battery, dye-sensitized solar cell, organic electroluminescent cell and electrolytic capacitor (all claimed).    ADVANTAGE - The composite polymer electrolyte composition containing fluorinated polymer is nonflammable and has improved lithium ion migration coefficient. The film formed using composite polymer electrolyte composition has excellent plasticity and tensile strength.    DETAILED DESCRIPTION - A molten salt monomer having quaternary ammonium salt structure comprising quaternary ammonium cation and anion, and polymerizable functional group is graft-polymerized onto polymer (a) having fluorine-containing repeating unit of formula: -(CR1R2-CFX)- (I), to obtain fluorinated polymer.    X=halo other than fluoro;and    R1,R2=H or fluoro.    INDEPENDENT CLAIMS are included for the following:    (1) composite polymer electrolyte composition, which contains the fluorinated polymer;    (2) lithium ion battery or lithium ion capacitor, which contains the composite polymer electrolyte composition between the negative electrode and positive electrode;    (3) polymer electrolytic membrane fuel cell battery, which comprises the composite polymer electrolyte composition positioned between the negative electrode and positive electrode;    (4) dye-sensitized solar cell, which contains composite polymer electrolyte composition positioned between working electrode which has the oxide semiconductor film to which the pigment is adsorbed, and an electroconductive counter electrode;    (5) organic electroluminescent cell, which has electron carrying layer arranged between the electroconductive electrodes which confront, and the light emitting layer containing an organic material with the composite polymer electrolyte composition; and    (6) electrolytic capacitor, which contains composite polymer electrolyte composition which does not include the charge-transfer ion source arranged between electroconductive electrodes.