Abstract: A redox flow battery which includes a battery cell to which a positive-electrode electrolyte and a negative-electrode electrolyte are supplied; a plurality of positive-electrode electrolyte tanks that store the positive-electrode electrolyte; a plurality of negative-electrode electrolyte tanks that store the negative-electrode electrolyte; a positive-electrode electrolyte tank switching device that switches a positive-electrode electrolyte tank among the plurality of positive electrolyte tanks; a negative-electrode electrolyte tank switching device that switches a negative-electrode electrolyte tank among the plurality of negative-electrode electrolyte tanks; a polarity switching unit that switches the polarity of the electrodes of the battery cells; and a controller for controlling switching the polarity of the electrodes, switching of the plurality of positive-electrode electrolyte tanks and switching of the plurality of negative-electrode electrolyte tanks.