A redox flow battery system (1, 2, 3, 4, 5) comprising: a plurality of branch circuits (10A, 10B) electrically connecting a plurality of battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) in parallel, the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) comprising a cell stack; a switching unit configured to switch conduction states of a closed loop in which the branch circuits (10A, 10B) are connected together; a circulation mechanism (20A, 20B, 20n) including a tank (21, 22) configured to store an electrolyte, and a pump (23, 24) configured to circulate the electrolyte from the tank (21, 22) to the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n); a detection unit configured to detect physical quantities correlating with open circuit voltages of the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n); a determination unit configured to determine, on a basis of the physical quantities detected by the detection unit, as to whether or not a voltage difference between the open circuit voltages of the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) is more than a predetermined value; and a control unit configured to control a switching operation of the switching unit such that, when the determination unit determines the voltage difference to be more than the predetermined value, the closed loop is brought into a non-conducting state and, when the determination unit determines the voltage difference to be equal to or less than the predetermined value, the closed loop is brought into a conducting state. a plurality of branch circuits (10A, 10B) electrically connecting a plurality of battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) in parallel, the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) comprising a cell stack; a switching unit configured to switch conduction states of a closed loop in which the branch circuits (10A, 10B) are connected together; a circulation mechanism (20A, 20B, 20n) including a tank (21, 22) configured to store an electrolyte, and a pump (23, 24) configured to circulate the electrolyte from the tank (21, 22) to the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n); a detection unit configured to detect physical quantities correlating with open circuit voltages of the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n); a determination unit configured to determine, on a basis of the physical quantities detected by the detection unit, as to whether or not a voltage difference between the open circuit voltages of the battery cell parts (12A, 12A 1, 12A 2, 12A n, 12B, 12B 1, 12B 2, 12B n) is more than a predetermined value; and a control unit configured to control a switching operation of the switching unit such that, when the determination unit determines the voltage difference to be more than the predetermined value, the closed loop is brought into a non-conducting state and, when the determination unit determines the voltage difference to be equal to or less than the predetermined value, the closed loop is brought into a conducting state.