The present invention provides (1) a thermopolymerizable composition containing a thermopolymerizable compound having (meth)acrylate having a moiety consisting of oxyalkylene, fluorocarbon, oxyfluorocarbon and / or carbonate group within the molecule, an electrolyte salt, an organic polymerization initiator having no benzene ring, and a polymerization retarder having vinyl group within the molecule, (2) a solid electrolyte obtained by heat-curing the composition, (3) a primary battery, a secondary battery and an electric double-layer capacitor each using the solid electrolyte, and processes for manufacturing the same.