Abstract: A swing drive system for a construction machine enhances safety for an operator. A swing control means 55A has a lever input amount-torque table 11 and an actual rotating speed-torque table 13. Based on a lever input amount and an actual rotating speed of an electric motor, the tables are used to derive torque values. A minimum value of the torque values is taken as the acceleration torque. The swing control means 55A further has a lever input amount-meter-out restriction area table 15 and an actual rotating speed-relief torque table 119. Based on the lever input amount and the actual rotating speed of the electric motor, a meter-out restriction area is derived from the lever input amount-meter-out restriction area table and the actual rotating speed to calculate a meter-out torque. A minimum value of the meter-out torque and relief torque is taken as the braking torque.