1. A battery management apparatus for grasping a change in impedance of a battery to reflect the battery management, the apparatus comprising: impedance calculating means for calculating the impedance of the battery using the terminal voltage of the battery, the open circuit voltage thereof, and the current thereof as parameters when a variation in current of the battery and the temperature thereof are respectively within predetermined ranges; and impedance correction value calculating means for comparing the impedance obtained by the impedance calculating means with an initial impedance previously obtained from the initial state of the battery to calculate an impedance correction value depending on the degree of deterioration of the battery.