A hybrid work machine comprising: an engine; a hydraulic pump driven by the engine; a plurality of hydraulic actuators (24a to 24h) driven by a hydraulic fluid delivered from the hydraulic pump; a plurality of operation devices (25a to 25h) provided within an operation room and issuing commands regarding operations of the plurality of hydraulic actuators (24a to 24h); an engine speed designation device that designates a target engine speed of the engine; a governor device that controls a fuel injection amount of the engine in such a manner that an engine speed of the engine is changed in response to the target engine speed of the engine and an output power torque of the engine increases as a load torque of the engine increases; a generator motor coupled to the engine; an electric storage device that supplies and receives electric power to and from the generator motor; and a first controller section configured to actuate the generator motor as an electric motor by supplying the electric power from the electric storage device to the generator motor to perform output power assist, and to actuate the generator motor as a generator by driving the generator motor to rotate by the engine to charge the electric storage device, and a gate lock lever that is provided within the operation room, and that is selectively operated to one of a lock position at which the operations of the plurality of hydraulic actuators (24a to 24h) by the plurality of operation devices (25a to 25h) are disabled and an unlock position at which the operations of the plurality of hydraulic actuators (24a to 24h) by the plurality of operation devices (25a to 25h) are enabled; a forced charging switch; characterized in that the hydraulic work machine further comprises: a work machine monitor that notifies an operator that a charging rate of the electric storage device defined as a ratio of an electric storage amount to a capacity of the electric storage device falls to be lower than a preset critical charging rate; and a second controller section configured to increase the target engine speed of the engine from a low idle engine speed to an engine speed suited for forced charging and actuate the generator motor as the generator in this state to forcedly charge the electric storage device when the gate lock lever is operated to the lock position, the engine speed designation device designates the low idle engine speed, and the forced charging switch is operated. an engine; a hydraulic pump driven by the engine; a plurality of hydraulic actuators (24a to 24h) driven by a hydraulic fluid delivered from the hydraulic pump; a plurality of operation devices (25a to 25h) provided within an operation room and issuing commands regarding operations of the plurality of hydraulic actuators (24a to 24h); an engine speed designation device that designates a target engine speed of the engine; a governor device that controls a fuel injection amount of the engine in such a manner that an engine speed of the engine is changed in response to the target engine speed of the engine and an output power torque of the engine increases as a load torque of the engine increases; a generator motor coupled to the engine; an electric storage device that supplies and receives electric power to and from the generator motor; and a first controller section configured to actuate the generator motor as an electric motor by supplying the electric power from the electric storage device to the generator motor to perform output power assist, and to actuate the generator motor as a generator by driving the generator motor to rotate by the engine to charge the electric storage device, and a gate lock lever that is provided within the operation room, and that is selectively operated to one of a lock position at which the operations of the plurality of hydraulic actuators (24a to 24h) by the plurality of operation devices (25a to 25h) are disabled and an unlock position at which the operations of the plurality of hydraulic actuators (24a to 24h) by the plurality of operation devices (25a to 25h) are enabled; a forced charging switch; characterized in that the hydraulic work machine further comprises: a work machine monitor that notifies an operator that a charging rate of the electric storage device defined as a ratio of an electric storage amount to a capacity of the electric storage device falls to be lower than a preset critical charging rate; and a second controller section configured to increase the target engine speed of the engine from a low idle engine speed to an engine speed suited for forced charging and actuate the generator motor as the generator in this state to forcedly charge the electric storage device when the gate lock lever is operated to the lock position, the engine speed designation device designates the low idle engine speed, and the forced charging switch is operated. a work machine monitor that notifies an operator that a charging rate of the electric storage device defined as a ratio of an electric storage amount to a capacity of the electric storage device falls to be lower than a preset critical charging rate; and a second controller section configured to increase the target engine speed of the engine from a low idle engine speed to an engine speed suited for forced charging and actuate the generator motor as the generator in this state to forcedly charge the electric storage device when the gate lock lever is operated to the lock position, the engine speed designation device designates the low idle engine speed, and the forced charging switch is operated.