To provide a power supply backup system which has high reliability and can backup a battery at a low cost.

An ACPI (Advanced Configuration and Power Interface) system 100 comprises: a memory module 130 (memory); a main power supply 110 for outputting a power determination signal showing that the power is fed to the memory and a standby signal of 5V indicating a migration to a power saving mode; an ACPI controller 150 for outputting an S3 control signal showing that the migration to the power saving mode is instructed; a DUAL circuit 180 for switching the power fed from the main power supply 110 to low power consumption in the power saving mode; an auxiliary power supply 170 that can feed the power toward the memory; and a battery control part 160 which monitors output states of the power determination signal from the main power supply 110 and the S3 control signal from the ACPI controller 150 and can control power feeding from the auxiliary power supply 170.

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