TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The components (S and I) contain conjugated diene-type polymer (P1) or vinyl polymer (P2). The polymer (P1) is obtained by polymerizing a monomer containing conjugated diene-type monomer (in mass%) (50 or more). The polymer (P2) is obtained by polymerizing a monomer containing monofunctional ethylenically unsaturated monomer (50 or more). The binder contains nonconjugated polyfunctional ethylenically unsaturated monomer (0.1-10) in insoluble component (I) of the vinyl polymer. Preferred Process: The polymer (A) is obtained by polymerizing polymerizable monomer mixture containing several components (I), and polymerizable monomer mixture containing several component (S). The binder is obtained by polymerizing monomer mixture which contains conjugated diene-type monomer by adding chain transfer agent (0-0.3) to the monomer mixture, and further polymerizing monomer mixture by adding chain transfer agent (0.4-2) to the monomer mixture. EXAMPLE - 28 mass% lauryl sulfate soda aqueous solution (in mass parts) (7.1), sodium tripolyphosphate (0.8) and deionized water (674.9), were stirred under nitrogen atmosphere and heated at 75degreesC. 2.44 mass% ammonium persulfate aqueous solution (82) was added to the reaction solution. 2-ethyl hexyl acrylate (EHA) (40), styrene (ST) (8.5) and ethylene glycol dimethacrylate (EDMA) (2) were added to the resulting solution for 2 hours, and polymerized, to obtain a polymer having particle diameter of 90 nm. Butyl acrylate (BA) (19), methyl methacrylate (MMA) (29) and methacrylic acid (MAA) (2), were added to the resulting solution for 2 hours, and reacted at 80degreesC for 3 hours, to obtain a binder consisting of aqueous polymer dispersion having particle diameter of 110 nm and solid content concentration of 40 mass%. An electrochemical element composition was obtained using the binder. The obtained composition provided cast film with polycarbonate solubility of 1% or less. A capacitor electrode having thickness of 120 microns and density of 0.63 g/cm3 was obtained using the composition. The obtained electrode had capacitance of 60.2 F/gr and peeling strength of 0.09 N/m.