A battery management system (BMS) includes a cell balancing circuit. The cell balancing circuit includes a reference voltage generator that is coupled in parallel to at least one battery and generates a reference voltage, a comparator that compares a voltage output from a terminal of the battery with the reference voltage output from the reference voltage generator, and a transistor that discharges a current from the battery, when turned-on in response to a signal outputted from the comparator, through a discharge resistor coupled in series to the battery.