The present invention provides a solid polymer electrolyte; a polymerizable composition having low viscosity and excellent processability for obtaining the solid polymer electrolyte; and a polymerizable compound having low viscosity, and good polymerizability and stability for use in the polymerizable composition. The present invention also provides primary and secondary batteries capable of working with high capacity and current; an electric double-layer capacitor ensuring high output voltage, large takeout current, and good processability; and an electrochromic device favored with high response speed. Each thereof use the solid polymer electrolyte of the present invention and are ensured with long life, excellent safety free of liquid leakage, high reliability and production at a low cost. A solid polymer electrolyte, including a carbonate-based polymer in which a branched chain is introduced and having a high dielectric constant and a wide electrochemical stability range, having excellent processability, good safety and high ionic conductivity, is provided.