PURPOSE:To provide a lithium battery of the electrolytic solution circulation type, which has a simple construction and a control function of keeping the output voltage thereof constant during the discharge thereof, by providing a circulated solution quantity control function in an electrolytic solution circulator for circulating an electrolytic solution in the battery, to increase the circulated quantity thereof as the discharge progresses. CONSTITUTION:A negative electrode 1 and a positive electrode 3 are coupled to each other with an interposed electroconductive plate 2 to constitute a bipolar electrode unit. Such bipolar electrode units are piled together. A desired output voltage is taken out through battery output terminals 4. An electrolytic solution circulator 5 is controlled so that an electrolytic solution taken in through an electrolytic solution inlet port 6 in activating a battery is poured into the circulator, the circulation of the solution is started, and the circulated quantity of the solution is less at the initial stage of discharge and increased along with the progress of the discharge. The quantity of the solution circulated through the battery is thus controlled to prevent the flow velocity of the circulated solution from falling due to the increase in the distance between the negative and the positive electrodes 1, 3 under the consumption of the negative electrode during the discharge, to keep the flow velocity constant. This results in preventing the output voltage of the battery from falling.