An apparatus for calculating remaining capacity of a battery is provided with a current detection section to detect current flow in the battery, a remaining capacity calculation section to integrate the current value detected by the current detection section and calculate remaining capacity, and a memory section to store discharge current within a specified current range. When current detected by the current detection section is within a specified range, the remaining capacity calculation section uses current values stored in the memory section, rather than values detected by the current detection section, as discharge current to calculate remaining capacity.