Hybrid Work Machine

A hybrid work machine is configured with an engine , a hydraulic pump , a hydraulic actuator, a generator motor coupled to the engine , an electric storage device that transmits and receives electric power to and from the generator motor , an engine controller that controls the engine based on a target engine revolution speed, a power controller that controls action of the generator motor , a controller that controls the engine controller and the power controller , and a target engine revolution speed change instructing device that give instructions on a change in the target engine revolution speed. The controller controls the engine controller and the power controller to act the generator motor as a generator until an actual revolution speed of the engine is reduced to a revolution speed corresponding to a target engine revolution speed after change if the target engine revolution speed has been changed to be lower while the engine is in an unloaded state. It is thereby possible to suppress noise of the engine in the case where the target engine revolution speed has been changed to be lower while the engine is in an unloaded state.