PURPOSE: To prevent erasion of the storage contents of a storage device by providing the battery storing devices in the number larger than those needed by at least ≥1 pieces.

CONSTITUTION: This device contains the battery storing devices 1 and 2, a controller 3, a RAM (occasional write/read memory) 4 which stores information, an information display device 5, and an information input device 6. Both devices 1 and 2 are set in parallel. When the batteries are replaced, a new battery is put into the device 2 while the old battery is kept in the device 1. Then the old battery is taken out of the device 1. Thus it is possible to avoid such a case where the stored information is erased when the old battery is taken out for replacement. In such a way, the information once stored is preserved.