PURPOSE: To prolong operating time by effectively utilizing a battery by storing the selection setting information of a resume mode/boot mode in a register and intermittently controlling a voltage output for backup corresponding to these stored contents.

CONSTITUTION: When the boot mode is selectively set, the set information is stored and held through a system BIOS 4 into a RAM 3, and the information is transmitted from the system BIOS 4 to the relevant register of a system gate array 1. A power source controller 9 of a power supply circuit 2 performs access through an internal interface 12 and an interface 8 to the system gate array 1 and according to the contents in the relevant register, it is recognized that the boot mode is set. On the condition of turning-off the power source of a system such as operating a power supply switch to the OFF side, for example, this is detected by the power source controller 9, and the output of the backup voltage due to a backup voltage output circuit 11 is stopped through an FET 10.