the opening roll 5 and which may be raised or lowered in a vertical direction relative to the tower 18 considering fig1 and 3 together to the rocker 9 at a distance from the pivot shaft 11 there is attached one end of the piston rod of a pneumatic cylinder 12 which at its opposite end is secured to an inner wall 2a of the housing accommodating the opening device the cylinder 12 is connected through a transducer 13 with a control device 14 which in turn is connected to a hoisting motor 15 for the cantilever 19 and the motor 16 for driving the carriage 17 a memory 20 and an inputting device 21 are connected with the control device 14 the memory 20 and the inputting device 21 apply predetermined signals to the control device 14 for the stepwise adjustment of the vertical setting of the bale supporting elements such as the pressing rolls 6a 6b as well as the vertical feed motion of the cantilever 19 by means of the hoisting motor 15 and the travel motion of the carriage 17 by means of the motor 16 turning to fig2 a and 2b to the pressing rolls 6a and 6b there are connected respective pneumatic cylinders 12a and 12b which exert vertical forces to roll supporting bars 12c 12d in the direction of arrows g h and i k respectively in fig2 a the pressing rolls 6a 6b are arranged in a horizontal plane a while in fig2 b the pressing roll 6a has been displaced in the direction of the.