To combine load applied by a primary cylinder with load applied by a secondary cylinder by incorporating a specified valve device for controlling a fluid flow between two cylinders.

A pressure fluid in an accumulator 20 is supplied through a fluid coupling 30, a filter 34 and a regulator 36 to a control valve 52 by the operation of an on/off switch 32. When the control valve 52 is put in the illustrated position, the pressure fluid is supplied to solenoids 42, 50 to put valves 40, 46 in the illustrated postitions. The valve 46 forces pressure fluid to flow through a port 78 into the right part of a chamber 72 of a cylinder 16, thereby elastically pressing a piston 82 to the left and releasing the fluid in the left side of a chamber 92 of a cylinder 18 through a valve 46 to the atmosphere. A solenoid valve 42 puts a valve 40 in the illustrated position, thereby transferring the pressure fluid in the left of the piston 82 from the chamber 72 to the right of the chamber 92, whereby load applied by piston rods 116 and 122 is increased to intensify the pressure.