Redox flow battery system

The present invention provides a redox flow cell system comprising: a cell that is charged or discharged due to the supply of an electrolyte; a monitor cell to which the same electrolyte is supplied; a current measurement unit for measuring a current input to or output from the cell; a voltage measurement unit for measuring the open-circuit voltage of the monitor cell; and an arithmetic unit for calculating the charging state of the electrolyte. The arithmetic unit includes a first processing unit, a second processing unit, and a third processing unit; the first processing unit calculates an integrated value by integrating current values measured by the current measurement unit over a period corresponding to a predetermined time constant; the second processing unit calculates a voltage correction value on the basis of the voltage values measured by the voltage measurement unit and the integrated value; the third processing unit computes the value of a first charging state of the electrolyte from the voltage c