A pump control unit for mounting on a redox flow battery system, the redox flow battery system including: a battery cell; electrolyte tanks (20,30); circulation pipes (25,35) for circulating and supplying electrolytes from the electrolyte tanks to the battery cell; pumps arranged to circulate the electrolytes through the circulation pipes; a power converter which is connected to the battery cell for controlling charging and discharging; an SOC measuring unit is arranged to measure the state of charge of the electrolytes; and a terminal-voltage measuring unit arranged to measure a terminal voltage of the battery cell, the pump control unit, is arranged to control the flow rate of the pumps, and comprises: a reference-flow-rate acquiring unit arranged to acquire a reference flow rate of the pumps corresponding to the state of charge of the electrolytes; a terminal-voltage determination unit arranged to determine whether or not the terminal voltage of the battery cell reaches the lower limit or the upper limit of a predetermined voltage range; and a pump-flow-rate setting unit arranged to set the reference flow rate for the pumps in the case where the terminal voltage does not reach the upper or lower limit of the predetermined voltage range, and set a flow rate obtained by adding a predetermined flow rate to the reference flow rate for the pumps in the case where the terminal voltage reaches the upper or lower limit of the predetermined voltage range. a battery cell; electrolyte tanks (20,30); circulation pipes (25,35) for circulating and supplying electrolytes from the electrolyte tanks to the battery cell; pumps arranged to circulate the electrolytes through the circulation pipes; a power converter which is connected to the battery cell for controlling charging and discharging; an SOC measuring unit is arranged to measure the state of charge of the electrolytes; and a terminal-voltage measuring unit arranged to measure a terminal voltage of the battery cell, the pump control unit, is arranged to control the flow rate of the pumps, and comprises: a reference-flow-rate acquiring unit arranged to acquire a reference flow rate of the pumps corresponding to the state of charge of the electrolytes; a terminal-voltage determination unit arranged to determine whether or not the terminal voltage of the battery cell reaches the lower limit or the upper limit of a predetermined voltage range; and a pump-flow-rate setting unit arranged to set the reference flow rate for the pumps in the case where the terminal voltage does not reach the upper or lower limit of the predetermined voltage range, and set a flow rate obtained by adding a predetermined flow rate to the reference flow rate for the pumps in the case where the terminal voltage reaches the upper or lower limit of the predetermined voltage range. a reference-flow-rate acquiring unit arranged to acquire a reference flow rate of the pumps corresponding to the state of charge of the electrolytes; a terminal-voltage determination unit arranged to determine whether or not the terminal voltage of the battery cell reaches the lower limit or the upper limit of a predetermined voltage range; and a pump-flow-rate setting unit arranged to set the reference flow rate for the pumps in the case where the terminal voltage does not reach the upper or lower limit of the predetermined voltage range, and set a flow rate obtained by adding a predetermined flow rate to the reference flow rate for the pumps in the case where the terminal voltage reaches the upper or lower limit of the predetermined voltage range.