To adjust position of a side wall and a slip of paper easily adjusting them to size of the slip of paper and eliminate necessity for removing a back plate when a continuous paper is carried on a bottom plate.

In a stacker mechanism for mounting slips of paper on a bottom plate 8 by inserting new slip of paper between the bottom plate 8 and a lowest slip of paper on the bottom plate 8, a side wall 37 for positioning width direction of the slip of paper and a back plate 38 for positioning a tip of the slip of paper are included and the side wall 37 is slidabie to the width direction of the slip of paper and the back plate 38 is fit to the side wall 37 and movable to a position contacting with the bottom plate 8 and a position apart from the bottom plate 8 and movable to the carriage direction of the slip of paper with it being contacted with the bottom plate 8. Whereby, the side wall 37 and the back plate 38 are positioned by sliding the side wall 37 and the back plate 38 adjusting them to size of the slip of paper and the bottom plate 8 is separated from the back plate 38 with them fit to the side wall 37.