PURPOSE: To maintain the parallelism of a slide by master and slave control by actuating specific one piece of hydraulic cylinder as a master when an unequal load is below the pressurizing capacity and the hydraulic cylinder of the largest load as a master when the unequal load exceeds the pressurizing capacity.

CONSTITUTION: For example, the pulses of a pulse generator 11 outputted by a microcomputer 10 act as a command value for lowering the slide and the respective hydraulic cylinders z extend to lower the slide 1. The displacement of the slide 1 causes the pulses of a linear scale 4 to be counted by a counter 12. The count value is fed back to a servo control system 16 which controls the respective hydraulic cylinders 2 until the deviation from the command value attains a specified value. Further, other three pieces of the hydraulic cylinders 2 are so controlled as to have the zero deviation from the specific one piece of the hydraulic cylinder 2' by comparing this deviation. The hydraulic cylinder of the severest load condition is actuated as the master to lower the slide 1 by the master and slave when the unequal load exceeds the pressurizing capacity.