To obtain the subject electrolyte having high ionic conductivity and free from the increase in the internal resistance by introducing an electron- attracting group into the molecular main chain and converting the product into an alkali metal salt.

This electrolyte is an alkali metal salt having an electron- attracting group in the molecular main chain and having a polymerization degree of preferably 10-1,000,000. It is a polymer composed of monomer units of the formula I to the formula V (M is an alkali metal; Y1 to Y4 are each independently SO2, CO, etc.; R1 and R2 are each independently a 1-5C alkylene, a halogenated alkylene or a direct bond; X is O, COO, NH, etc.; R3 and R4 are each independently a 1-5C alkyl, a halogenated alkyl, a direct bond, etc.; Y3-R3 and Y4-R4 are each CHO, NO2, etc.) or a copolymer composed of two or more kinds of the above monomer units. Since the polymer bas an electron- attracting group in the main chain, the delocalization of the anionic charge is promoted and the cationic charge transfer is accelerated to improve the ionic conductivity.