An object of the invention is to provide a tetrafluoroborate producing method that allows high-yield, high-efficiency production of a tetrafluoroborate by a continuous process, a tetrafluoroborate-containing electrolyte, and an electrical storage device including such an electrolyte. The invention provides a method for producing a tetrafluoroborate, which includes: a first step including dissolving boron trifluoride gas in an organic solvent; a second step including adding, to the organic solvent, a fluoride (MFn, wherein M represents a metal or NH4, and 1≦n≦3) in an amount stoichiometrically equivalent to or less than the amount of the boron trifluoride so that a tetrafluoroborate solution is produced; and a third step including circulating the tetrafluoroborate solution through the first step so that the boron trifluoride gas is dissolved in the tetrafluoroborate solution instead of the organic solvent.