Abstract: A hybrid construction machine includes a hydraulic pressure work element driven by hydraulic pressure generated by driving power of an internal combustion engine or a motor generator, and also includes an electric-motor work element driven by an electric motor. A superordinate control unit generates a control command which controls drive of the hydraulic pressure work element and the electric-motor work element. A subordinate control unit controls drive of the hydraulic pressure work element and the electric-motor work element based on the control command generated by the superordinate control unit. The subordinate control unit monitors an error in the superordinate control unit.