To secure important data in a memory and to practically perform power supply control of a main power supply or further a device including a backup feeding system.

Backup power supply is fed to a memory 113 storing the important data from a battery 14 at a power supply trouble. By using one circuit at a contact of the main switch 18 for supplying or disconnecting the main power supply of the device and by linking with the main switch 18, when the main switch 18 disconnects the main power supply, the feeding of backup power supply to the memory 113 from the battery 14 is stopped to reduce the number of the charging and discharging cycles of the battery 14, to prevent the deterioration of the battery 14 and to extend the life of the battery 14. On the other hand, a soft switch 18a for controlling the main switch 18 is provided, and the disconnection operation of the main power supply is controlled in accordance the existence/no-existence of the important data in the memory 113 when the soft switch 18a performs a disconnection operation of the main power supply.