A rotation drive control unit configured to control the driving of the rotation mechanism of a construction machine driven to rotate by an electric motor includes a speed command output part configured to output a speed command controlling the rotation speed of the electric motor based on the amount of operation input via the operation part of the construction machine; a torque direction detection part configured to detect the direction of torque applied on the rotation shaft of the rotation mechanism; and a drive control part configured to generate a drive command driving the electric motor based on the speed command output from the speed command output part and to control the driving of the electric motor, wherein in starting rotation of the rotation mechanism, the drive control part starts driving the electric motor using the drive command if the direction of the rotation represented by the speed command output from the speed command output part and the direction of the torque detected by the torque direction detection part are opposite directions.