Macromolecular solid electrolyte consists of a complex contg. a polymer obtd. from at least one cpd. of formula (1) and/or a copolymer using the cpd. of formula (1) as a copolymerising component and at least one electrolyte.    CH2 = C(R1)-CO-[O(CH2)x(CH(CH3))y]z-NH-CO-OR2 (1)    R1 = H, or a methyl gp.; R2 = an organic chain contg. at least one oxyalkylene gp.; The organic chain may be straight- or branched-chain, or cyclic structure, and may contain at least one element except carbon, hydrogen, and oxygen; x and y = 0 or 1-5; z = 0 or 1-10; when x = 0, and y = 0, z is 0; (CH2) and (CH(CH3)) in [O(CH2)x(CH(CH3))y]z may be irregularly arranged. A plasticiser may be added to the macromolecular solid electrolyte.    Also claimed is a battery using the macromolecular solid electrolyte.    Also claimed is prodn. of the battery comprising: (a) filling or placing a polymerising monomer mixt. contg. at least one cpd. of formula (1), and at least one electrolyte, or a polymerising monomer mixt. formed of the polymerising monomer mixt. mentioned above, and a plasticiser in a structure for constituting the battery or on a support; and (b) polymerising the polymerising monomer mixt.    Also claimed is an electrical double layer solid capacitor (condenser) having polarising electrodes through an ion-conductive substance. The ion-conductive substance consists of the macromolecular solid electrolyte.    Also claimed is prodn. of the electrical double layer solid capacitor (condenser) comprising: (a) filling or placing a polymerising monomer mixt. contg. at least one cpd. of formula (1), and at least one electrolyte, or a polymerising monomer mixt. formed of the polymerising monomer mixt. mentioned above, and a plasticiser in a structure for constituting the electrical double layer solid capacitor (condenser) or on a support; and (b) polymerising the polymerising monomer mixt.    USE -   The macromolecular solid electrolyte is used for batteries and the electrical double layer solid capacitors (condensers). The battery is used in portable electrical devices, backup power supplies, electric cars and road levelling.    ADVANTAGE -   The macromolecular solid electrolyte is readily formed in a thin film having good film strength and high ion conductivity. The battery and the capacitor (condenser) have no liq. leakage and continuous stability. Thin batteries and the thin capacitors (condensers) can be produced.