A power supply device includes a power conversion circuit, a secondary battery, and a control circuit. The power conversion circuit converts alternating-current or direct-current power into direct-current power to supply power to a load. The secondary battery is connected between the power conversion circuit and the load and charged with power from the power conversion circuit so that power is supplied to the load when the charging power is discharged. The control circuit controls the power supply device to perform a first operation that, after the charging of the secondary battery, supply of input power into said power conversion circuit is halted and the secondary battery supplies the power accumulated by said charging to said load.