PURPOSE: To control a loop amount smoothly and small with an inexpensive control device by accelerating and decelerating uncoiling rollers in a manner as to keep the loop amount within a predetermined intermediate region and changing the speed to a mean speed before and after the acceleration or deceleration when it coms within the intermediate region.

CONSTITUTION: When a loop 5 deviates upward from an intermediate region M, it is detected by a photoelectric switch 11 for detecting loop position, and an uncoiling roller 3 is accelerated by a motor 2 via an electric circuit so that the loop 5 is returned from the accelerating region A into the intermediate region M. When it deviates downward, it is detected with a photoelectric switch 10 and a roller 3 is decelerated so that the loop is returned from the decelerating region D to the intermediate region. However, in this state, the loop 5 passes by the intermediate region M in a short time and will keep oscillating between the regions A and D indefinitely. Therefore, the device is so arranged that, when the loop 5 enters the region M, the roller 3 is revolved at the mean speed of the speeds before and after the acceleration and deceleration at the accelerating and decelerating.