In a hybrid construction machine, its display device displays, toward an operator, an artificial engine sound serving as load information according to a magnitude of a workload, instead of an engine sound. Furthermore, the display device issues an alarm sound to surrounding workers when performing an operation by only stored electrical power of an electrical energy storage device without using an engine. In this hybrid construction machine, in addition to the issuing of alarm from the display device during the operation without using the engine, the display device issues an advance notice sound for engine restart when at least one value out of the workload and a charge amount of the electrical energy storage device has become an advance notice set value close to a set value of engine restart.