In a battery control device for controlling input to and output from a battery pack of the present invention, the battery pack includes a plurality of serially-connected battery blocks each including a plurality of serially-connected unit batteries. The device includes: an internal resistance measurement section for each battery block; and a first malfunctioning battery detection section for detecting the unit battery as a leakage malfunctioning battery based on an internal resistance variation measured for each battery block during a prescribed time interval of a charging operation, wherein detection information about the leakage malfunctioning battery is reflected in the control of charging and discharging operations.