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 a voltage value within a certain range; and a variable voltage charge storage part configured to tolerate a variation in a voltage value 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.