Disclosed is a swing control apparatus of construction machinery, including: a hydraulic pump discharging working oil for driving a swing motor and controlling a discharge flux according to an input pump command value Vpump; a pressure sensor sensing pressure of the working oil discharged from the hydraulic pump; and a control unit calculating the pump command value Vpump based on a swing operation quantity Vsw input from the swing operation unit to output the calculated pump command value to the hydraulic pump, wherein when the input swing operation quantity Vsw is larger than a preset reference swing operation quantity Vswo and the discharge pressure Ppump of the hydraulic pump detected by the pressure sensor is lower than a first reference pressure Pswr1, the control unit calculates a converted swing operation quantity Vsw′ gradually increasing from the reference swing operation quantity Vswo to the input swing operation quantity Vsw and calculates the pump command value Vpump of the hydraulic pump corresponding to the converted swing operation quantity Vsw′.