To provide a hybrid type construction machine in which work can be kept on even if the amount of electricity stored in an electric storage device is out of an appropriate value. Both a hydraulic motor 27 and an electric motor 25 are provided for driving an upper swing structure 20. When the amount of electricity stored in a capacitor 24 is appropriate, the upper swing structure 20 is driven by both the hydraulic motor 27 and the electric motor 25. When the amount of electricity stored in the capacitor 24 exceeds an appropriate value, the mode is changed over to a mode in which the upper swing structure 20 is driven only by the hydraulic motor 27, and an assist electric generation motor 23 is assist-driven or engine-driven to thereby rapidly return the amount of electricity stored in the capacitor 24 to an appropriate range. The capacity of the capacitor 24 can be reduced, and the amount of electricity stored in the capacitor can be managed without losing the operability of swing motion.