A battery pack that detects the voltage of a plurality of batteries (1) connected in series with a plurality of voltage detection circuits (2). When a voltage detection circuit output is HIGH, batteries (1) discharge through an output resistor (6). In addition, discharge circuits (7), which are series connections of balance resistors (8) and switching devices (9), are connected in parallel with batteries (1) left "un-discharged" by the output resistors (6). When a voltage detection circuit output is HIGH, some batteries (1) are discharged by the output resistor (6) and the "un-discharged" batteries (1) are discharged by the discharge circuit (7). When a voltage detection circuit output is LOW, no batteries (1) are discharged by the output resistor (6) and the "un-discharged" batteries (1) are also left un-discharged by the discharge circuit (7) to balance the discharge currents of all the batteries (1).