A lithium-ion battery pack, despite having a simple circuit configuration, allows the charge amount of the individual battery cells provided therein to be made uniform quickly. For each battery cell, a cell balance circuit is provided that includes a resistor, a transistor, and a control circuit. The resistor and the transistor are connected in series, with their end terminals connected to the two terminals of the battery cell. The control circuit controls the state of the transistor so that the two terminals of the battery cell are short-circuited through the resistor when necessary. The control circuit includes an oscillation circuit for producing a sawtooth wave voltage that oscillates within a predetermined voltage range and outputting it after adding it to the voltage at the negative terminal of the battery cell, and a comparator for comparing the voltage at the positive terminal of the battery cell with the voltage output from the oscillation circuit and outputting, when the former exceeds the latter, a control voltage that makes the transistor conduct. When the cell voltage is within the range of the voltage produced by the oscillation circuit, the transistor is driven with a pulse-width-modulated driving voltage.