To manufacture a battery pack at a low cost, which exactly detects remaining capacity of each battery pack even in a state where a plurality of battery packs are used.

An electric device has a battery pack 20 which has a secondary battery 21 inside, and a body device 10 which mounts the battery pack 20. The body device 10 has a current detection circuit 11 and an A/D converter 13 which converts a detected current signal into a digital value. The battery pack 20 has inside a capacity calculation circuit 22 which calculates the remaining capacity of the secondary battery 21 by integrating current detected in the body device 10. The electric device converts the current of the battery pack 20 detected by the current detection circuit 11 of the body device 10 to the digital value by the A/D converter 13, and transmits it to the capacity calculation circuit 22 of the battery pack 20; and the capacity calculation circuit 22 calculates the remaining capacity of secondary battery 21.