PURPOSE: To prevent the slip of a drum by increasing the frictional force between the drum and an under roller by pressing roller onto the upper part of the drum loaded onto the under roller.

CONSTITUTION: The both edges of a pressing roller 19 are rotatably supported onto a pair of arms 20, and the basic edge part of said arm 20 is rotatably supported at the upper edge of a pair of stays 21 erected from a base 18. When a hydraulic cylinder 22 is extended, the pressing roller 19 is lifted up as shown by the alternating dotted line, and the accommodation of a drum 11 is permitted, and when the hydraulic cylinder 22 is contracted, the pressing roller 19 is pressed onto the upper part of the drum 11. When the pressing force is represented by F, if F is selected as follows: T<M(W+F), the slip of the drum 11 is prevented.