A secondary battery control device having a sleep mode includes a current detection element for detecting a charging/discharging current value of a battery, a voltage detection element for detecting an open-circuit voltage value of the battery, and a control section for calculating the remaining capacity of the battery based on the detected values. When the control section enters the sleep mode, the control section sets, in a wake timer, based on the remaining battery capacity and the discharging current value at this time, an amount of time required for the remaining battery capacity to reach a predetermined value (about 5%), as an amount of time required for the control section to be restored to a normal mode. When the set amount of time has passed, the control section is restored to the normal mode, and corrects the remaining battery capacity to obtain an accurate remaining battery capacity.