Abstract: In a fuel-cells system 10 including a stack of fuel cells 20 and a storage battery 30, the remaining charge of the storage battery 30 is measured by a remaining charge monitor 46. In case that the observed remaining charge of the storage battery 30 is less than a predetermined reference value, a control unit 50 outputs a driving signal to an inverter 80, in order to restrict the consumption of electric power by a motor 32. When it is determined that the output state of the storage battery 30 is in the discharging state, based on the output electric current of the storage battery 30 measured by a current sensor 90, the control unit 50 further limits the electric power consumed by the motor 32. These processes are repeatedly carried out to charge the storage battery 30 and recover the remaining charge of the storage battery 30 to a sufficient level.