Construction machinery which is capable of improving fuel efficiency of the engine and also capable of effectively utilizing surplus energy in a light-load mode. The construction machinery includes an engine, a hydraulic pump driven by the engine, and actuators driven by oil pressure supplied from the hydraulic pump. In the light-load mode where the engine torque at the intersection point of an iso-horsepower curve of the necessary horsepower and a governor characteristic curve of the engine is smaller than that of a rated output point of the engine, the number of revolutions of the engine is reduced while the engine torque is increased with respect to the intersection point, and the horsepower is made to exceed the iso-horsepower curve. With surplus torque generated therefrom, a power generator is operated so as to generate electric power, which is stored in a power accumulation apparatus.