PURPOSE: To achieve smooth ram movement, accurate lower stop limit and high synchronization accuracy by providing a pair of right and left mechanical servo-valves for controlling up-down movement of ram cylinders.

CONSTITUTION: With the start of descend of the ram, drum wound wires 19 and 20 put drums 13 and 14 in synchronized revolution. A command input to the servo-motor 7 causes the ram 3 turning at a high speed to rapidly descend from the upper limit position down to a position immediately before the variable speed position. When the ram comes before the set lower limit, the motor 7 given a command revolves at a low speed, turning the ball screws 11 and 12 at a low speed. A difference in revolution speed between the ball screws 11 and 12 and turning drums 13 and 14 driven by wires which feed-back descending movement of the ram moves the drums 13 and 14 a little in the advance direction, operating turning levers 15 and 16 to slowly close fully opened servo-valves 17 and 18. This decreases flow rate of the oil fed to the ram cylinder 4, lowering the ram 3 at a low speed from the variable speed position to the lower limit position. Thus, a work is bent at both a low speed and a high speed.