An Uninterruptible Power Supply UPS for supplying a power source to a load which requires the UPS, the UPS comprising: a commercial power source unit configured to supply a first power source to the load; a battery configured to supply a second power source to the load; a power failure monitoring unit configured to monitor a power failure state in the commercial power source unit; a charging/discharging determination unit configured to determine a charging state of the battery and to estimate remaining capacity of the battery; a power source control unit configured to control the commercial power source unit and the battery in response to output of the power failure monitoring unit or the charging/discharging determination unit so that the first power source or the second power source is supplied to the load; and an operation time setting unit configured to set a peak time zone of the load; wherein the power source control unit, when the first power source is normal and it is the peak time zone, is operable to divide and supply the first power source and the second power source to the load, while the second power source is supplied within an available remaining battery capacity except for an essential remaining capacity of a battery that needs to be essentially maintained in an emergency, wherein the power source control unit, when the first power source is cut off and when it is not the peak time zone, is operable to control the second power source to be supplied to the load, wherein the power source control unit, when the first power source is normal, is operable to control the second power source to be supplied to the load, wherein the power source control unit is operable to determine whether it is possible to supply only the available remaining battery capacity to the load during the peak time zone, and when it is impossible to supply only the available remaining battery capacity to the load, the power source control unit is operable to calculate a current capacity that may continue to be discharged uniformly during the peak time zone using only the available remaining battery capacity and supply the calculated current capacity to the load during the peak time zone such that the second power source is shared with the first power source to be supplied to the load. a commercial power source unit configured to supply a first power source to the load; a battery configured to supply a second power source to the load; a power failure monitoring unit configured to monitor a power failure state in the commercial power source unit; a charging/discharging determination unit configured to determine a charging state of the battery and to estimate remaining capacity of the battery; a power source control unit configured to control the commercial power source unit and the battery in response to output of the power failure monitoring unit or the charging/discharging determination unit so that the first power source or the second power source is supplied to the load; and an operation time setting unit configured to set a peak time zone of the load; wherein the power source control unit, when the first power source is normal and it is the peak time zone, is operable to divide and supply the first power source and the second power source to the load, while the second power source is supplied within an available remaining battery capacity except for an essential remaining capacity of a battery that needs to be essentially maintained in an emergency, wherein the power source control unit, when the first power source is cut off and when it is not the peak time zone, is operable to control the second power source to be supplied to the load, wherein the power source control unit, when the first power source is normal, is operable to control the second power source to be supplied to the load, wherein the power source control unit is operable to determine whether it is possible to supply only the available remaining battery capacity to the load during the peak time zone, and when it is impossible to supply only the available remaining battery capacity to the load, the power source control unit is operable to calculate a current capacity that may continue to be discharged uniformly during the peak time zone using only the available remaining battery capacity and supply the calculated current capacity to the load during the peak time zone such that the second power source is shared with the first power source to be supplied to the load.