There is provided construction machinery for switchably controlling rotational speed between a normal and an energy saving mode. Change in workload is detected by means except for change in pressure of a main circuit. It is more convenient to use the machinery in the energy saving mode, increasing opportunities for use in the energy saving mode to suppress fuel consumption and noise. An engine controlling device for construction machinery for switchably controlling the rotational speed of an engine between a normal mode in the range of a higher rotational speed and an energy saving mode in therange of a lower rotational speed includes a vehicle speed sensor, an ECM for controlling the rotational speed of the engine, and an on-board controller for sending a command signal to the ECM basedon the value detected by the vehicle speed sensor to switch the rotational speed of the engine to either the normal mode or the energy saving mode; wherein when a vehicle speed is changed by workloadin the energy saving mode to be lower than a predetermined range, the on-board controller commands the ECM to switch the rotational speed of the engine to the normal mode.