A storage battery control device detects an overhead wire supply current value showing a sum of a current value output from a storage battery and a current value output from a transformer substation, and charging or discharging of the storage battery is controlled so that a charging rate of the storage battery becomes a charging rate target value when the detected overhead wire supply current value is less than a first threshold. In addition, charging or discharging of the storage battery is controlled so that the output voltage of the storage battery control device is maintained at a constant voltage control mode when the detected overhead wire supply current value is greater than or equal to the first threshold.