PURPOSE: To correct snaking of a web due to slip at a let-out section and a large let-out resistance, at a let-out position.

CONSTITUTION: Driving shafts 1a, 1a at both let-out parts 1, 1 are respectively connected to output ends 2a, 2a of a differential gear mechanism 2, and an input end 2c of the differential gear mechanism 2 is connected to a driving source 3. When one let-out part 1 slips, and the frictional resistance decreases, or when the tension on one side of a web W becomes smaller than the tension on the opposite side, and the revolutions of one driving shaft 1a increases, the revolutions of the other driving shaft 1a is reduced as many as the increased revolutions by the operation of the differential gear mechanism 2, to reduce the let-out quantity on the side of the web W where slip did not take place, or on the side with a larger tension. Then, when the slipping stops, or the difference in the tension at both side parts W1, W1 of the web W is eliminated, both driving shafts 1a, 1a rotate at the same speed, and both side parts W1, W1 of the web W is evently let out.