A switching power supply unit which contains a secondary battery for backup and a circuit for controlling the charging and discharging of the secondary battery in its enclosure and which properly manages the charging and discharging of the secondary battery. A switching power supply circuit includes a rectifying and smoothing circuit for smoothing alternating-current input from commercial power supply Vin at normal operation time, a battery pack charged by a DC—DC converter which can continuously output a predetermined direct-current power supply voltage for supplying power supply voltage to the DC—DC converter at the time of a stoppage in alternating-current input, a charging circuit section for controlling the charging and discharging of the battery pack, and a charging and discharging control circuit. The battery pack and circuits, such as the DC—DC converter, are mounted in the same unit enclosure.