Hybrid construction machinery, comprising: an engine; a hydraulic pump that is driven by the engine; a hydraulic working unit (16-3, 4, 5) that is driven by pressure oil discharged from the hydraulic pump; a motor generator that transmits torque between the engine; an electrical storage apparatus that feeds electric power to the motor generator; and a controller that controls the engine with a governor characteristic in which the relation between load torque and rotational speed has such predetermined inclination that the rotational speed reduces as the load torque increases, wherein the controller includes: a governor characteristic changing unit that changes setting of the governor characteristic; a load power calculating unit that calculates load power on an engine shaft; an electrical storage remaining amount calculating unit that calculates a remaining amount of the electrical storage apparatus; a charge/discharge request calculating unit that calculates a charge/discharge request required for keeping electric power of the electrical storage apparatus in a proper range based on an output of the electrical storage remaining amount calculating unit; a target engine power calculating unit that calculates target power of the engine; a target rotational speed calculating unit that calculates a target rotational speed command of the motor generator; and a motor generator control unit that controls the motor generator according to a target rotational speed command value calculated by the target rotational speed calculating unit, wherein the target engine power calculating unit calculates first target engine power that increases and decreases according to increase and decrease of an output value from the load power calculating unit and the charge/discharge request calculating unit, and wherein the target rotational speed calculating unit calculates rotational speed of an intersection point of a governor characteristic line changed by the governor characteristic changing unit and an equal power line dependent on the first target engine power on a rotational speed-torque characteristic diagram as a target rotational speed command value of the motor generator. an engine; a hydraulic pump that is driven by the engine; a hydraulic working unit (16-3, 4, 5) that is driven by pressure oil discharged from the hydraulic pump; a motor generator that transmits torque between the engine; an electrical storage apparatus that feeds electric power to the motor generator; and a controller that controls the engine with a governor characteristic in which the relation between load torque and rotational speed has such predetermined inclination that the rotational speed reduces as the load torque increases, a governor characteristic changing unit that changes setting of the governor characteristic; a load power calculating unit that calculates load power on an engine shaft; an electrical storage remaining amount calculating unit that calculates a remaining amount of the electrical storage apparatus; a charge/discharge request calculating unit that calculates a charge/discharge request required for keeping electric power of the electrical storage apparatus in a proper range based on an output of the electrical storage remaining amount calculating unit; a target engine power calculating unit that calculates target power of the engine; a target rotational speed calculating unit that calculates a target rotational speed command of the motor generator; and a motor generator control unit that controls the motor generator according to a target rotational speed command value calculated by the target rotational speed calculating unit, wherein the target engine power calculating unit calculates first target engine power that increases and decreases according to increase and decrease of an output value from the load power calculating unit and the charge/discharge request calculating unit, and wherein the target rotational speed calculating unit calculates rotational speed of an intersection point of a governor characteristic line changed by the governor characteristic changing unit and an equal power line dependent on the first target engine power on a rotational speed-torque characteristic diagram as a target rotational speed command value of the motor generator.