A hybrid construction machine including an internal combustion engine, a motor generator, a hydraulically driven working element, and a rotation mechanism rotationally driven by a rotation electric motor includes a charge storage part provided between the motor generator and the rotation electric motor, wherein the charge storage part includes a constant voltage charge storage part configured to maintain its voltage value within a certain range; and a variable voltage charge storage part configured to tolerate a variation in the voltage value of the charge storage part due to the electric motor and the generator operation of the motor generator or the power running and the regenerative operation of the rotation electric motor.