An apparatus for balancing a battery according to the present disclosure includes: a voltage measuring unit configured to measure a voltage of each of a plurality of battery cells connected to each other; and a control unit configured to calculate a state of charge (SOC) of each of the battery cells from the voltage measured by the voltage measuring unit, select a standard cell and a target group on the basis of the calculated SOCs of the battery cells, choose one battery cell among battery cells belonging to the selected target group as a target cell, calculate a balancing time according to a difference between the SOC of the standard cell and the SOC of the target cell, and perform balancing to the battery cells belonging to the target group during the calculated balancing time.