by solid lines in fig2 whereby the expansion bar 6 is disposed at a position indicated by solid lines in fig1 parenthetically it should be mentioned that temple means not shown for preventing shrinkage crepe of the woven fabric w in the direction widthwise thereof as well as a fell plate not shown either for preventing lowering of the fabric in the vicinity of the cloth fell w1 are so arranged as to follow the displacement of the expansion bar 6 further the reciprocative displacement of the driven nut members 20a and 20b is transmitted to the tension roller 12 via the trifurcated intermediate lever 13 and the rod 15 at this juncture it should also be noted that the sliding load such as observed in a worm mechanism is absent between the ball screw 18a and the driven nut members 20a and 20b and they are only subjected to a rolling load which is remarkably smaller than the sliding load thus the efficiency of driving power transmission from the ball screw 18a to the driven nut members 20a and 20b is significantly enhanced when compared with that of the worm mechanism for this reason an inexpensive electric motor of small capacity can be employed as the servo motor 18 which thus provides an advantage in respect to the cost over the prior art machine in which the worm mechanism is employed besides.