Secondary cells and electrical double-layer capacitors of excellent charge-discharge efficiency, stability and low-temperature properties can be obtained using nonaqueous electrolytes which contain an ionic liquid that has general formula (1) below and is liquid at not higher than 50.degree. C. and an ion-conductive polymer. ##STR00001## In formula (1), R.sup.1 to R.sup.4 are each independently an alkyl group of 1 to 5 carbons or an alkoxyalkyl group of the formula R'--O--(CH.sub.2).sub.n-- (R' being methyl or ethyl, and the letter n being an integer from 1 to 4), and any two from among R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may together form a ring, with the proviso that at least one of R.sup.1 to R.sup.4 is an alkoxyalkyl group of the above formula. X is a nitrogen atom or a phosphorus atom, and Y is a monovalent anion.