A hybrid construction machine according to the present invention includes a controller for controlling an engine with a droop characteristic. The controller includes: a target engine output calculation unit (2-4) that calculates a target output of the engine; a target speed setting unit (2-7) that sets a target speed command of a motor-generator; a target droop calculation unit (2-8) that obtains an intersection point of a constant output line with the target output value of the engine and a constant speed line with the target speed command of the motor-generator on a speed-torque characteristic diagram, and determines a governor characteristic of the engine so that the governor characteristic passes through the intersection point; a governor characteristic changing unit (2-10) that changes the governor characteristic of the engine; and a motor-generator control unit (2-9) that controls the motor-generator in accordance with the target speed command value.