BACKUP POWER SUPPLY DEVICE AND POWER OUTPUT METHOD

A backup power supply device configured to supply an electric power for backup to an optical encoder 11 when a main power supply 13 for driving the optical encoder 11 breaks down, the backup power supply device comprises: a battery 12 configured to storage a DC power; a capacitor 33 configured to storage a DC power, the capacitor 33 configured to supply an electric power for backup to the optical encoder 11 when the battery 12 cannot supply the electric power thereof; a discharge device 34 configured to discharge the electric power charged in the battery 12; and a periodical discharge controller 35 configured to perform control to intermittently output the electric power charged in the battery 12 to the discharge device 34 to consume the battery power.