Electrical storage devices having excellent low-temperature properties can be obtained by using a quaternary salt (or ionic liquid) of general formula (1) below as an electrolyte salt for electrical storage devices or a liquid electrolyte for electrical storage devices. ##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--, with the proviso that at least one group from among R.sup.1 to R.sup.4 is the above alkoxyalkyl group. X is a nitrogen or phosphorus atom, and Y is a monovalent anion.