A device, mounted on a hydraulic
excavator, for allowing each of first and second electric motors (13), (14) to generate power by using
electric power supplied from a power supply having a predetermined capacity, and actuating a boom cylinder (6), an arm cylinder (7), etc. using the generated power. The device is characterized by comprising
electric motor controllers (24), (25), etc. for respectively controlling power that is generated by the electric motors (13), (14) so that, in
machine-operation, powers generated by the electric motors (13), (14) may be equal to or less than predetermined rated outputs, and that the total amount of powers generated simultaneously by the electric motors (13), (14) may correspond to the maximum capacity of the power supply, so as to prolong the
time of use with high thrust and
high torque without increasing the capacitors of the electric motors (13), (14) and power supply.