Agent for forming gel electrolyte, composition for forming gel electrolyte, gel electrolyte, and electricity storage device

This agent for forming a gel electrolyte contains a polymer (A) which has a repeating unit (A1) that is derived from a (meth)acrylate having a cyclic ether structure and a repeating unit (A2) that is derived from a (meth)acrylate having a chain ether structure, with the ratio of the amount (M2 [mol%]) of the repeating unit (A2) relative to the amount (M1 [mol%]) of the repeating unit (A1), namely M2/M1 being within the range of 1-10 when the total amount of the repeating unit (A1) and the repeating unit (A2) is taken as 100 [mol%].