Provided is a hybrid construction machine preventing an electrical storage device from overcharge, including a hydraulic actuator, a hydraulic pump, a generator-motor which performs electric generator and motor actions, an engine, an electric actuator which generates regenerative electric power, an electrical storage device which performs a charge-and-discharge action with the generator-motor and the electric actuator, a charge-rate detector which detects a charge rate C1 of the electrical storage device, and a control section which controls an operation of the generator-motor and a charge-and-discharge action of the electrical storage device. The control section, when the charge rate C1 exceeds a set value Cs, performs overcharge-prevention control of making assist power by the electric motor action of the generator-motor be greater than that when C1≦Cs, the set value Cs predetermined as a charge rate at which receiving the regenerative electric power can overcharge the electrical storage device.