An apparatus for equalization of a battery pack that is composed of plural battery cells, comprising: a cell balancing device equalizing the voltages of the plural battery cells; a battery cell monitor monitoring the voltage and/or current of each battery cell; a correction voltage calculator calculating correction voltage for a subject battery cell that needs to be equalized, based on the monitored voltage and/or current of the subject battery cell, characterized in that the correction voltage is calculated based on the internal resistance of the subject battery cell; and the apparatus further comprises a cell balancing controller determining the subject battery cell from the plural battery cells, wherein the cell balancing controller corrects target voltage for equalization of the subject battery cell by the calculated correction voltage, and the cell balancing controller causes the cell balancing device to execute equalization of the subject battery cell so that the monitored voltage of the subject battery cell reaches the corrected target voltage, wherein the cell balancing device takes charge from one or more battery cells and delivers the charge to one or more of the remaining battery cells so as to equalize the voltages of the plural battery cells, and the cell balancing controller calculates an ending voltage by subtracting the calculated correction voltage from the target voltage which is an average voltage of the plural battery cells when the subject battery cell needs to be discharged, and the cell balancing controller calculates the ending voltage by adding the calculated correction voltage to the target voltage which is an average voltage of the plural battery cells when the subject battery cell needs to be charged. a cell balancing device equalizing the voltages of the plural battery cells; a battery cell monitor monitoring the voltage and/or current of each battery cell; a correction voltage calculator calculating correction voltage for a subject battery cell that needs to be equalized, based on the monitored voltage and/or current of the subject battery cell, characterized in that the correction voltage is calculated based on the internal resistance of the subject battery cell; and the apparatus further comprises a cell balancing controller determining the subject battery cell from the plural battery cells, wherein the cell balancing controller corrects target voltage for equalization of the subject battery cell by the calculated correction voltage, and the cell balancing controller causes the cell balancing device to execute equalization of the subject battery cell so that the monitored voltage of the subject battery cell reaches the corrected target voltage, wherein the cell balancing device takes charge from one or more battery cells and delivers the charge to one or more of the remaining battery cells so as to equalize the voltages of the plural battery cells, and the cell balancing controller calculates an ending voltage by subtracting the calculated correction voltage from the target voltage which is an average voltage of the plural battery cells when the subject battery cell needs to be discharged, and the cell balancing controller calculates the ending voltage by adding the calculated correction voltage to the target voltage which is an average voltage of the plural battery cells when the subject battery cell needs to be charged.