The battery management system of the present invention measures a cell voltage of a battery more efficiently using a small number of elements, and measures a pack current and voltage thereof when measuring the voltages of a plurality of cells. The battery management system is coupled to the battery formed with one pack having a plurality of battery cells. The battery includes a first sub-pack having first and second batteries among the plurality of battery cells. The battery management system includes first to fourth relays and an A/D converter. The first and the second relays transmit the cell voltages in response to respective first and second control signals by being coupled to each output terminal of the first and second battery cells of the first sub-pack. The third relay transmits the cell voltage transmitted though one of the first and second relays in response to a third control signal, and the first charging unit stores the cell voltage transmitted from the third relay. The fourth relay transmits the cell voltage stored in the first charging unit in response to a fourth control signal. The A/D converter converts the cell voltages transmitted through the fourth relay into digital data.