PURPOSE: To smoothly perform the freely detachable linking action of each upper surface place pawl for each groove of a transfer drum by arranging a plurality of grooves on the outside of the transfer drum, and concurrently providing each pawl guiding tapered section gradually inclined toward the grooves at both banks for each projected upper end between the grooves.

CONSTITUTION: An upper surface plate starts descending, and when the paired pawls 6 of the upper surface plate approach to the upper end of each groove 7 over the outside of a transfer drum, the descent of the upper surface plate permits each pawl 6 to be engaged with each groove 7, so that the freely detachable linking action of the upper surface plate to the transfer drum is thereby performed. In this case, if each pawl 6 of the upper surface plate is out of the extension line of each groove 7 over the outside of the transfer drum, each pawl 6 is guided by pawl guiding tapered sections 12 at projected upper ends on both the sides of each groove 7 so as to be smoothly led into the aforesaid groove 7. Besides, each pawl 6 of the upper surface plate is guided to each groove along the pawl guiding tapered section 12 by each rolling roller 13 so as to be smoothly led into the aforesaid groove 7.