A battery state judging apparatus comprising a voltage detector detecting a voltage at a terminal of a battery, a current detector detecting a charge/discharge current of the battery and an arithmetic operation circuit calculating a residual capacity index of the battery relating to a value obtained by subtracting a quantity of electric charge from a reference capacity value of the battery and calculating a power consumption of the battery from the detected terminal voltage and charge/discharge current. The arithmetic operation circuit estimates a charge/discharge current as a function of the battery residual capacity index and battery power consumption and successively estimates a charge/discharge current in a predetermined power consumption pattern to successively calculate a battery residual capacity index from the estimated charge/discharge current. A battery operable threshold is judged when a battery discharge current, estimated on the basis of an updated battery residual capacity index exceeds a threshold current at that power consumption, and a result is displayed via a display circuit.