A swing control circuit is provided separately from a hydraulic actuator control circuit. The swing control circuit includes a swing pump motor connected to closed circuits of a swing motor through a solenoid valve that serves as a directional control valve. A swing motor generator is connected to the swing pump motor. The swing motor generator is connected to an electric power storage device of a hybrid type drive system. An exterior-connecting passage for feeding hydraulic fluid to hydraulic actuators of a lower structure and a work equipment is drawn from a pipeline between the swing pump motor and the solenoid valve. A connecting passage solenoid valve is disposed in the exterior-connecting passage. The invention enables hydraulic energy generated in the swing system to be directly fed to the outside of the swing system.