Final state-of-charge calculation means is provided which calculates a final state-of-charge of the battery according to state-of-charge estimate values by electric current integration mode state-of-charge estimation means and equivalent circuit model mode state-of-charge estimation means. The final state-of-charge calculation means performs, when a difference between the state-of-charge estimate value by the electric current integration mode state-of-charge estimation means and the state-of-charge estimate value by the equivalent circuit model mode state-of-charge estimation means becomes less than or equal to the state-of-charge difference threshold value, switching of the final state-of-charge from the state-of-charge estimate value by the electric current integration mode state-of-charge estimation means to the state-of-charge estimate value by the equivalent circuit model mode state-of-charge estimation means.