An abnormal cell detection method of a battery pack including a plurality of cells according to the present disclosure includes: obtaining a first discharge rate for each cell during a first rest period in a state where cell balancing is allowed; prohibiting the cell balancing of the plurality of cells when a cell having the first discharge rate greater than or equal to a first threshold value is detected; obtaining a second discharge rate during a second rest period for each cell in a state where the cell balancing is prohibited; and detecting a cell having a second discharge rate greater than or equal to a second threshold value among the plurality of cells as an abnormal cell.