Abstract: An input/output control device for a secondary battery mounted on a vehicle includes a current estimating unit estimating a battery current input to or output from the secondary battery based on an input/output power of the secondary battery and outputting an estimated value (estimated current (Is)), a current sensor measuring the battery current and outputting a measured value (measured current (It)), and an input/output control unit controlling the input/output power based on the estimated value and the measured value. The input/output control device controls the input/output of the secondary battery, using the measured current (It) as well as the estimated value (Is), and therefore can suppress more reliably significant increase in heating value of the secondary battery and its peripheral parts.