A construction machine comprising: an engine; a hydraulic pump of the variable displacement type which is driven by the engine; a swing structure; a swing hydraulic motor which drives the swing structure by using hydraulic fluid delivered from the hydraulic pump; an electrical storage device which stores and supplies electric power; a swing electric motor which drives the swing structure by using the electric power supplied from the electrical storage device; a swing control lever which is operated for commanding the driving of the swing structure; a delivery capacity regulating device which regulates the delivery capacity of the hydraulic pump; a control unit which controls the driving/braking of the swing structure by using a sum total of torque of the swing hydraulic motor and torque of the swing electric motor by driving both the swing hydraulic motor and the swing electric motor when the swing control lever is operated; an operation amount detection device which detects the operation amount of the swing control lever; and a speed detection device which detects the speed of the swing electric motor; characterized in that the control unit includes: a torque command value calculation unit which takes in the operation amount signal representing the operation amount of the swing control lever detected by the operation amount detection device and the speed signal representing the speed of the swing electric motor detected by the speed detection device and calculates a torque command value for the swing electric motor based on the operation amount signal and the speed signal; a hydraulic pump output reduction control unit which controls the delivery capacity regulating device by calculating the reduction rate of the output of the hydraulic pump based on the torque command value for the swing electric motor calculated by the torque command value calculation unit, the operation amount signal regarding the swing control lever and the speed signal regarding the swing electric motor, wherein: the hydraulic pump output reduction control unit calculates the reduction rate of the output of the hydraulic pump to be high when the operation amount of the swing control lever is a fine operation less than a prescribed operation amount, and the hydraulic pump output reduction control unit calculates as a lower value with the increase in the operation amount of the swing control lever when the operation amount exceeds the prescribed operation amount. a torque command value calculation unit which takes in the operation amount signal representing the operation amount of the swing control lever detected by the operation amount detection device and the speed signal representing the speed of the swing electric motor detected by the speed detection device and calculates a torque command value for the swing electric motor based on the operation amount signal and the speed signal; a hydraulic pump output reduction control unit which controls the delivery capacity regulating device by calculating the reduction rate of the output of the hydraulic pump based on the torque command value for the swing electric motor calculated by the torque command value calculation unit, the operation amount signal regarding the swing control lever and the speed signal regarding the swing electric motor, wherein: the hydraulic pump output reduction control unit calculates the reduction rate of the output of the hydraulic pump to be high when the operation amount of the swing control lever is a fine operation less than a prescribed operation amount, and the hydraulic pump output reduction control unit calculates as a lower value with the increase in the operation amount of the swing control lever when the operation amount exceeds the prescribed operation amount.