A control device for a secondary battery includes an offset addition unit calculating an offset amount based on a plurality of voltage values sensed by a sensor, the number of a plurality of battery cells included in one battery block and a preset range, and adding an offset amount to the sensed voltage values, when a flag is turned on to indicate the fact the voltage value of one of the battery cells falls within a preset range, and also includes an I/O control unit controlling charge/discharge of the battery based on voltage values containing the offset amount added thereto. Even when the battery voltage is sensed a battery block at a time, the voltage value can be controlled a cell at a time.