BACKUP POWER-SUPPLY DEVICE

A backup power-supply device (3) including a control unit (35) is provided. In a case where a main power supply is normal when an ignition is turned on, the control unit (35) controls to turn on or off a charging circuit (32) to charge a capacitor (31) from the main power supply (2) so that a voltage of the capacitor (31) becomes constant at a target voltage and turns off the discharging circuit (33) to stop discharging from the capacitor (31) to a first electronic device (4). In a case where an abnormality occurs in the main power supply (2) when the ignition is turned on, the control unit (35) turns off the charging circuit (32) to stop charging from the main power supply (2) to the capacitor (31) and turns on the discharging circuit (33) to perform discharging from the capacitor to the first electronic device (4). A first switch (S1) is provided between a second electronic device (5) and the capacitor (31). The control unit (35) turns on the discharging circuit (33) and the first switch (S1) and turns off the charging circuit (32) after the ignition is turned off to perform discharging from the capacitor (31) to the second electronic device (5).