To provide a fluttering-prevention device capable of surely cutting a paper sheet so that a tail can be formed, by preventing the paper sheet from fluttering and from separating from a tail cutter upon feeding the paper sheet to a paper machine.

Upon forming a tail Pt (shown in Fig.2) by cutting a paper sheet P using a tail cutter 13, a preventing rod 22 is turned from a waiting position (shown in Fig.1 by a broken line) to a preventing position (shown in Fig.1 by a solid line) in accordance with the action of turning a rotary knife 14b disposed on a waiting position (shown in Fig.1 by a broken line) to a cutting position (shown in Fig.1 by a solid line) to cause the preventing rod 22 to press and tension the paper sheet P. Thus, the fluttering of the paper sheet P is prevented, and the tail Pt is formed by cutting the paper sheet P by the rotary knife 14b of the tail cutter 13. In accordance with the travelling of the tail cutter 13 from the cutting position to the waiting position, the preventing rod 22 travels from the preventing position to the waiting position, and hence the paper sheet P is not hindered from travelling.