A battery pack control apparatus for monitoring a voltage of a plurality of series-connected cells (1a...d) constituting a battery pack and for determining a spontaneous change in a reference voltage, the battery pack control apparatus comprising: a voltage detecting means configured to detect a voltage of each cell in the plurality of cells; a plurality of reference voltage generating means (30, 31, 32, 33) configured to generate a corresponding reference voltage for each cell; a switching means comprising a plurality of voltage switching circuits provided for each cell and configured to generate a threshold voltage corresponding to a threshold from the voltage at a corresponding one of the cells (1a...1d) for each cell thereby relatively changing the reference voltage for each cell; a plurality of voltage comparing means (50, 51, 52, 53) configured to compare said threshold voltage of each cell received to the non-inverting input of the voltage comparing means (50, 51, 52, 53) with the corresponding reference voltage; and a determining means that: is configured to determine whether there is a spontaneous change of the reference voltage based on a comparison between: a result of the comparison between the voltage of each cell detected by the voltage detecting means and the corresponding reference voltage; and a result of the comparison by the voltage comparing means while the reference voltage is relatively changed stepwisely by the plurality of voltage switching circuits, wherein a range of relative change in the reference voltage by the plurality of switching circuits is set to a usage voltage range to be used by each cell within a total voltage range of each cell, the total voltage range being defined from a minimum voltage to a maximum voltage of each cell, and wherein there is no spontaneous change in the reference voltage when the corresponding compared results match each other and there is a spontaneous change in the reference voltage when the corresponding compared results do not match each other. a voltage detecting means configured to detect a voltage of each cell in the plurality of cells; a plurality of reference voltage generating means (30, 31, 32, 33) configured to generate a corresponding reference voltage for each cell; a switching means comprising a plurality of voltage switching circuits provided for each cell and configured to generate a threshold voltage corresponding to a threshold from the voltage at a corresponding one of the cells (1a...1d) for each cell thereby relatively changing the reference voltage for each cell; a plurality of voltage comparing means (50, 51, 52, 53) configured to compare said threshold voltage of each cell received to the non-inverting input of the voltage comparing means (50, 51, 52, 53) with the corresponding reference voltage; and a determining means that: is configured to determine whether there is a spontaneous change of the reference voltage based on a comparison between: a result of the comparison between the voltage of each cell detected by the voltage detecting means and the corresponding reference voltage; and a result of the comparison by the voltage comparing means while the reference voltage is relatively changed stepwisely by the plurality of voltage switching circuits, wherein a range of relative change in the reference voltage by the plurality of switching circuits is set to a usage voltage range to be used by each cell within a total voltage range of each cell, the total voltage range being defined from a minimum voltage to a maximum voltage of each cell, and wherein there is no spontaneous change in the reference voltage when the corresponding compared results match each other and there is a spontaneous change in the reference voltage when the corresponding compared results do not match each other. is configured to determine whether there is a spontaneous change of the reference voltage based on a comparison between: a result of the comparison between the voltage of each cell detected by the voltage detecting means and the corresponding reference voltage; and a result of the comparison by the voltage comparing means while the reference voltage is relatively changed stepwisely by the plurality of voltage switching circuits, a result of the comparison between the voltage of each cell detected by the voltage detecting means and the corresponding reference voltage; and a result of the comparison by the voltage comparing means while the reference voltage is relatively changed stepwisely by the plurality of voltage switching circuits, wherein a range of relative change in the reference voltage by the plurality of switching circuits is set to a usage voltage range to be used by each cell within a total voltage range of each cell, the total voltage range being defined from a minimum voltage to a maximum voltage of each cell, and wherein there is no spontaneous change in the reference voltage when the corresponding compared results match each other and there is a spontaneous change in the reference voltage when the corresponding compared results do not match each other.