Abstract: A system for automatically assembling or processing a large variety of parts of different weights. The system has a first industrial robot whose end having at least three degrees of freedom for movement in horizontal and vertical planes, and a second industrial robot whose end having at least three degrees of freedom for movement in horizontal and vertical planes. The first and second industrial robots are connected to each other by connecting means which carries a sensor adapted to sense the difference of vertical position between the connecting ends of the first and second industrial robots. The operation of the first and second industrial robots is under the control of a controller. The first industrial robot is operated by an instruction given by the controller, while the second industrial robot is operated to follow-up the movement of the first industrial robot, in accordance with the signal derived from the sensor.